Display device and manufacturing method thereof

ABSTRACT

Provided is a novel display device that is highly convenient or reliable or a display device with low power consumption and high display quality. The display device includes a first pixel and a second pixel. The first pixel and the second pixel are adjacent to each other. Each of the first pixel and the second pixel includes a first display region and a second display region. The first display region is configured to reflect incident light. The second display region is positioned inside the first display region and configured to emit light. A position of the second display region inside the first display region in the first pixel and a position of the second display region inside the first display region in the second pixel are different from each other.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device anda manufacturing method thereof.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specific examples of the technical field ofone embodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, a method for drivingany of them, and a method for manufacturing any of them.

BACKGROUND ART

A liquid crystal display device in which a surface-emitting light sourceis provided as a backlight and combined with a transmissive liquidcrystal display device in order to reduce power consumption and suppressa reduction in display quality is known (see Patent Document 1).

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2011-248351

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide anovel display device that is highly convenient or reliable.

Another object of one embodiment of the present invention is to providea display device with low power consumption and high display quality.Another object of one embodiment of the present invention is to providea novel display device.

Note that the description of these objects does not disturb theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a display device including afirst pixel and a second pixel. The first pixel and the second pixel areadjacent to each other. Each of the first pixel and the second pixelincludes a first display region and a second display region. The firstdisplay region is configured to reflect incident light. The seconddisplay region is positioned inside the first display region andconfigured to emit light. A position of the second display region insidethe first display region in the first pixel and a position of the seconddisplay region inside the first display region in the second pixel aredifferent from each other.

Another embodiment of the present invention is a display deviceincluding a first pixel and a second pixel. The first pixel and thesecond pixel are adjacent to each other. Each of the first pixel and thesecond pixel includes a first display region, a second display region, afirst display element, and a second display element. The first displayregion is configured to reflect incident light. The second displayregion is positioned inside the first display region and configured toemit light. The first display element is provided to overlap with thefirst display region. The second display element is provided to overlapwith the second display region. A position of the second display regioninside the first display region in the first pixel and a position of thesecond display region inside the first display region in the secondpixel are different from each other.

In the above structure, it is preferable that the first display elementinclude a liquid crystal layer and the second display element include alight-emitting layer.

In the above structure, colors of light emitted from the second displayelement in the first pixel and the second display element in the secondpixel are preferably different. In the above structure, it is preferablethat the first display element and the second display element beconnected to different transistors and independently controlled.

In the above structure, the transistor preferably includes an oxidesemiconductor film in a channel region.

In the above structure, the interval between the second display regionin the first pixel and the second display region in the second pixel ispreferably greater than or equal to 20 μm.

Another embodiment of the present invention is a display moduleincluding a touch sensor and the display device with any one of theabove structures.

Another embodiment of the present invention is an electronic deviceincluding a battery and the display device with any one of the abovestructures or the display module.

With one embodiment of the present invention, a novel display devicethat is highly convenient or reliable can be provided. With oneembodiment of the present invention, a display device with low powerconsumption and high display quality can be provided. With oneembodiment of the present invention, a novel display device can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a display region of a displayelement.

FIG. 2 is a schematic view illustrating a display region of a displayelement.

FIG. 3 is a schematic view illustrating a display region of a displayelement.

FIG. 4 is a schematic view illustrating a display region of a displayelement.

FIG. 5 is a circuit diagram illustrating a display device.

FIG. 6 is a circuit diagram illustrating pixels.

FIGS. 7A and 7B are top views illustrating a display device and pixels.

FIG. 8 is a cross-sectional view illustrating a display device.

FIG. 9 is a cross-sectional view illustrating a display device.

FIG. 10 is a cross-sectional view illustrating a display device.

FIG. 11 is a cross-sectional view illustrating a display device.

FIGS. 12A to 12C are cross-sectional views illustrating a manufacturingprocess of a display device.

FIGS. 13A to 13C are cross-sectional views illustrating a manufacturingprocess of a display device.

FIGS. 14A to 14C are cross-sectional views illustrating a manufacturingprocess of a display device.

FIGS. 15A to 15C are cross-sectional views illustrating a manufacturingprocess of a display device.

FIGS. 16A and 16B are cross-sectional views illustrating a manufacturingprocess of a display device.

FIG. 17 is a cross-sectional view illustrating a manufacturing processof a display device.

FIG. 18 is a cross-sectional view illustrating a display device.

FIG. 19 is a cross-sectional view illustrating a display device.

FIG. 20 is a cross-sectional view illustrating a display device.

FIG. 21 is a cross-sectional view illustrating a display device.

FIG. 22 is a cross-sectional view illustrating a display device.

FIG. 23 is a cross-sectional view illustrating a display device.

FIG. 24 is a cross-sectional view illustrating a display device.

FIG. 25 is a cross-sectional view illustrating a display device.

FIG. 26 is a cross-sectional view illustrating a display element.

FIGS. 27A to 27C are cross-sectional views illustrating a manufacturingmethod of a display element.

FIGS. 28A and 28B are cross-sectional views illustrating a manufacturingmethod of a display element.

FIGS. 29A to 29C are a top view and cross-sectional views illustrating asemiconductor device.

FIGS. 30A to 30C are a top view and cross-sectional views illustrating asemiconductor device.

FIGS. 31A and 31B are cross-sectional views illustrating a semiconductordevice.

FIGS. 32A and 32B are cross-sectional views illustrating a semiconductordevice.

FIGS. 33A and 33B are cross-sectional views illustrating a semiconductordevice.

FIGS. 34A and 34B are cross-sectional views illustrating a semiconductordevice.

FIGS. 35A and 35B are cross-sectional views illustrating a semiconductordevice.

FIGS. 36A to 36C illustrate band structures.

FIGS. 37A to 37C are a top view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 38A to 38C are a top view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 39A to 39C are a top view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 40A to 40C are a top view and cross-sectional views illustratingone embodiment of a transistor.

FIGS. 41A to 41D are cross-sectional views illustrating embodiments oftransistors.

FIGS. 42A to 42E show structural analysis results of a CAAC-OS and asingle-crystal oxide semiconductor by XRD and selected-area electrondiffraction patterns of a CAAC-OS.

FIGS. 43A to 43E show a cross-sectional TEM image and plan-view TEMimages of a CAAC-OS and images obtained through analysis thereof.

FIGS. 44A to 44D show electron diffraction patterns and across-sectional TEM image of an nc-OS.

FIGS. 45A and 45B show cross-sectional TEM images of an a-like OS.

FIG. 46 shows a change in crystal part of an In—Ga—Zn oxide induced byelectron irradiation.

FIG. 47 illustrates a display module.

FIGS. 48A to 48E illustrate electronic devices.

FIGS. 49A to 49E are perspective views illustrating a display device.

FIGS. 50A and 50B are perspective views illustrating a display device.

FIGS. 51A and 51B illustrate a structure of a data processor.

FIGS. 52A to 52C are cross-sectional views illustrating light-emittingelements in Example.

FIG. 53 is a graph showing luminance-current density characteristics oflight-emitting elements in Example.

FIG. 54 is a graph showing luminance-voltage characteristics oflight-emitting elements in Example.

FIG. 55 is a graph showing current efficiency-luminance characteristicsof light-emitting elements in Example.

FIG. 56 is a graph showing current-voltage characteristics oflight-emitting elements in Example.

FIG. 57 is a graph showing emission spectra of light-emitting elementsin Example.

FIGS. 58A to 58C are cross-sectional views illustrating light-emittingelements in Example.

FIG. 59 is a graph showing luminance-current density characteristics oflight-emitting elements in Example.

FIG. 60 is a graph showing luminance-voltage characteristics oflight-emitting elements in Example.

FIG. 61 is a graph showing current efficiency-luminance characteristicsof light-emitting elements in Example.

FIG. 62 is a graph showing current-voltage characteristics oflight-emitting elements in Example.

FIG. 63 is a graph showing emission spectra of light-emitting elementsin Example.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described below with reference to drawings. However,the embodiments can be implemented in many different modes, and it willbe readily appreciated by those skilled in the art that modes anddetails thereof can be changed in various ways without departing fromthe spirit and scope of the present invention. Thus, the presentinvention should not be interpreted as being limited to the followingdescription of the embodiments.

In the drawings, the size, the layer thickness, and the region areexaggerated for clarity in some cases. Therefore, embodiments of thepresent invention are not limited to such a scale. Note that thedrawings are schematic views showing ideal examples, and embodiments ofthe present invention are not limited to shapes or values shown in thedrawings.

Note that in this specification, ordinal numbers such as “first”,“second”, and “third” are used in order to avoid confusion amongcomponents, and the terms do not limit the components numerically.

Note that in this specification, terms for describing arrangement, suchas “over” “above”, “under”, and “below”, are used for convenience indescribing a positional relation between components with reference todrawings. Furthermore, the positional relation between components ischanged as appropriate in accordance with a direction in which eachcomponent is described. Thus, there is no limitation on terms used inthis specification, and description can be made appropriately dependingon the situation.

In this specification and the like, a transistor is an element having atleast three terminals of a gate, a drain, and a source. In addition, thetransistor has a channel region between a drain (a drain terminal, adrain region, or a drain electrode) and a source (a source terminal, asource region, or a source electrode), and current can flow through thedrain, the channel region, and the source. Note that in thisspecification and the like, a channel region refers to a region throughwhich current mainly flows.

Furthermore, functions of a source and a drain might be switched whentransistors having different polarities are employed or a direction ofcurrent flow is changed in circuit operation, for example. Therefore,the terms “source” and “drain” can be switched in this specification andthe like.

Note that in this specification and the like, the expression“electrically connected” includes the case where components areconnected through an “object having any electric function”. There is noparticular limitation on an “object having any electric function” aslong as electric signals can be transmitted and received betweencomponents that are connected through the object. Examples of an “objecthaving any electric function” are a switching element such as atransistor, a resistor, an inductor, a capacitor, and elements with avariety of functions as well as an electrode and a wiring.

In this specification and the like, the term “parallel” indicates thatthe angle formed between two straight lines is greater than or equal to−10° and less than or equal to 10°, and accordingly also includes thecase where the angle is greater than or equal to −5° and less than orequal to 5°. The term “perpendicular” indicates that the angle formedbetween two straight lines is greater than or equal to 80° and less thanor equal to 100°, and accordingly also includes the case where the angleis greater than or equal to 85° and less than or equal to 95°.

In this specification and the like, the terms “film” and “layer” can beinterchanged with each other. For example, in some cases, the term“conductive film” can be used instead of the term “conductive layer”,and the term “insulating layer” can be used instead of the term“insulating film”.

Unless otherwise specified, off-state current in this specification andthe like refers to drain current of a transistor in an off state (alsoreferred to as a non-conducting state and a cutoff state). Unlessotherwise specified, the off state of an n-channel transistor means thatthe voltage between its gate and source (V_(gs): gate-source voltage) islower than the threshold voltage V_(th), and the off state of ap-channel transistor means that the gate-source voltage V_(gs) is higherthan the threshold voltage V_(th). For example, the off-state current ofan n-channel transistor sometimes refers to drain current that flowswhen the gate-source voltage V_(gs) is lower than the threshold voltageV_(th).

The off-state current of a transistor depends on V_(gs) in some cases.Therefore, “the off-state current of a transistor is I or lower” maymean that the off-state current of the transistor is I or lower at acertain V_(gs). The off-state current of a transistor may refer tooff-state current at a given V_(gs), at V_(gs) in a given range, atV_(gs) at which sufficiently low off-state current is obtained, or thelike.

As an example, an assumption is made that an n-channel transistor has athreshold voltage V_(th) of 0.5 V and a drain current of 1×10⁻⁹ A atV_(gs) of 0.5 V, 1×10⁻¹³ A at V_(gs) of 0.1 V, 1×10⁻¹⁹ A at V_(gs) of−0.5 V, and 1×10⁻²² A at V_(gs) of −0.8 V. The drain current of thetransistor is 1×10⁻¹⁹ A or lower at V_(gs) of −0.5 V or at V_(gs) in therange of −0.8 V to −0.5 V; therefore, it may be said that the off-statecurrent of the transistor is 1×10⁻¹⁹ A or lower. Since the drain currentof the transistor is 1×10⁻²² A or lower at a certain V_(gs), it may besaid that the off-state current of the transistor is 1×10⁻²² A or lower.

In this specification and the like, the off-state current of atransistor with a channel width W is sometimes represented by a currentvalue per channel width W or by a current value per given channel width(e.g., 1 μm). In the latter case, the off-state current may berepresented by current per length (e.g., A/μm).

The off-state current of a transistor depends on temperature in somecases. Unless otherwise specified, the off-state current in thisspecification may be off-state current at room temperature, 60° C., 85°C., 95° C., or 125° C. Alternatively, the off-state current may beoff-state current at a temperature at which the reliability of asemiconductor device or the like including the transistor is ensured ora temperature at which the semiconductor device or the like includingthe transistor is used (e.g., a temperature in the range of 5° C. to 35°C.). The state in which the off-state current of a transistor is I orlower may indicate that the off-state current of the transistor at roomtemperature, 60° C., 85° C., 95° C., 125° C., a temperature at which thereliability of a semiconductor device or the like including thetransistor is ensured, or a temperature at which the semiconductordevice or the like including the transistor is used (e.g., a temperaturein the range of 5° C. to 35° C.) is I or lower at a certain V_(gs).

The off-state current of a transistor depends on the voltage V_(ds)between its drain and source in some cases. Unless otherwise specified,the off-state current in this specification may be off-state current atV_(ds) of 0.1 V, 0.8 V, 1 V, 1.2 V, 1.8 V, 2.5 V, 3 V, 3.3 V, 10 V, 12V, 16 V, or 20 V. Alternatively, the off-state current may be off-statecurrent at V_(ds) at which the reliability of a semiconductor device orthe like including the transistor is ensured or at V_(ds) used in thesemiconductor device or the like including the transistor. The state inwhich the off-state current of a transistor is I or lower may indicatethat the off-state current of the transistor at V_(ds) of 0.1 V, 0.8 V,1 V, 1.2 V, 1.8 V, 2.5 V, 3 V, 3.3 V, 10 V, 12 V, 16 V, or 20 V, atV_(ds) at which the reliability of a semiconductor device or the likeincluding the transistor is ensured, or at V_(ds) used in thesemiconductor device or the like including the transistor is I or lowerat a certain V_(gs).

In the above description of the off-state current, a drain may bereplaced with a source. That is, the off-state current sometimes refersto current that flows through a source of a transistor in the off state.

In this specification and the like, the term “leakage current” sometimesexpresses the same meaning as “off-state current”. In this specificationand the like, the off-state current sometimes refers to current thatflows between a source and a drain of a transistor in the off state, forexample.

In this specification and the like, a “semiconductor” includescharacteristics of an “insulator” in some cases when the conductivity issufficiently low, for example. Furthermore, a “semiconductor” and an“insulator” cannot be strictly distinguished from each other in somecases because a border between the “semiconductor” and the “insulator”is not clear. Accordingly, a “semiconductor” in this specification andthe like can be called an “insulator” in some cases. Similarly, an“insulator” in this specification and the like can be called a“semiconductor” in some cases. Alternatively, an “insulator” in thisspecification and the like can be called a “semi-insulator” in somecases.

In this specification and the like, a “semiconductor” includescharacteristics of a “conductor” in some cases when the conductivity issufficiently high, for example. Further, a “semiconductor” and a“conductor” cannot be strictly distinguished from each other in somecases because a border between the “semiconductor” and the “conductor”is not clear. Accordingly, a “semiconductor” in this specification andthe like can be called a “conductor” in some cases. Similarly, a“conductor” in this specification and the like can be called a“semiconductor” in some cases.

In this specification and the like, an impurity in a semiconductorrefers to an element that is not a main component of the semiconductor.For example, an element with a concentration of lower than 0.1 atomic %is an impurity. When an impurity is contained, the density of states(DOS) may be formed in a semiconductor, the carrier mobility may bedecreased, or the crystallinity may be decreased, for example. In thecase where the semiconductor includes an oxide semiconductor, examplesof an impurity which changes characteristics of the semiconductorinclude Group 1 elements, Group 2 elements, Group 14 elements, Group 15elements, and transition metals other than the main components;specifically, there are hydrogen (included in water), lithium, sodium,silicon, boron, phosphorus, carbon, and nitrogen, for example. In thecase of an oxide semiconductor, oxygen vacancy may be formed by entry ofimpurities such as hydrogen. Furthermore, when the semiconductorincludes silicon, examples of an impurity which changes thecharacteristics of the semiconductor include oxygen, Group 1 elementsexcept hydrogen, Group 2 elements, Group 13 elements, and Group 15elements.

In this specification and the like, pixels are dots that constitute animage and each pixel is a smallest unit of a color element that cancontrol the brightness. For example, in the case of a display deviceincluding RGB (R: red, G: green, and B: blue) color elements, an Rpixel, a G pixel, and a B pixel are a smallest unit of an image. Notethat depending on circumstances, the pixel is called a subpixel in somecases.

In this specification and the like, a blue wavelength range refers to awavelength range of greater than or equal to 400 nm and less than 490nm, and blue light emission has at least one emission spectrum peak inthe wavelength range. A green wavelength range refers to a wavelengthrange of greater than or equal to 490 nm and less than 550 nm, and greenlight emission has at least one emission spectrum peak in the wavelengthrange. A yellow wavelength range refers to a wavelength range of greaterthan or equal to 550 nm and less than 590 nm, and yellow light emissionhas at least one emission spectrum peak in the wavelength range. A redwavelength range refers to a wavelength range of greater than or equalto 590 nm and less than or equal to 740 nm, and red light emission hasat least one emission spectrum peak in the wavelength range.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention is described with reference to FIG. 1 to FIG. 25.

<1-1. Structure of Display Device>

First, the structure of a display device is described with reference toFIG. 5. A display device 500 illustrated in FIG. 5 includes a pixelportion 502, and gate driver circuit portions 504 a and 504 b and asource driver circuit portion 506 which are placed outside the pixelportion 502.

[Pixel Portion]

The pixel portion 502 includes pixel circuits 10(X, Y) arranged in Xrows (X is a natural number of 2 or more) and Y columns (Y is a naturalnumber of 2 or more). Each of the pixel circuits 10(X, Y) includes twodisplay elements having different functions. One of the two displayelements has a function of reflecting incident light, and the other hasa function of emitting light. Note that the details of the two displayelements are described later.

[Gate Driver Circuit Portion]

Some or all of the gate driver circuit portions 504 a and 504 b and thesource driver circuit portion 506 are preferably formed over a substrateover which the pixel portion 502 is formed. Thus, the number ofcomponents and the number of terminals can be reduced. In the case wheresome or all of the gate driver circuit portions 504 a and 504 b and thesource driver circuit portion 506 are not formed over the substrate overwhich the pixel portion 502 is formed, a separately prepared drivercircuit board (e.g., a driver circuit board formed using asingle-crystal semiconductor film or a polycrystalline semiconductorfilm) may be formed in the display device 500 by chip on glass (COG) ortape automated bonding (TAB).

The gate driver circuit portions 504 a and 504 b have a function ofoutputting a signal (a scan signal) for selecting the pixels 10(X, Y).The source driver circuit portion 506 has a function of supplying asignal (data signal) for driving the display elements included in thepixels 10(X, Y).

The gate driver circuit portion 504 a has a function of controlling thepotentials of wirings supplied with scan signals (hereinafter, suchwirings are referred to as scan lines G_(E) _(_) ₁ to G_(E) _(_) _(X))or a function of supplying an initialization signal. The gate drivercircuit portion 504 b has a function of controlling the potentials ofwirings supplied with scan signals (hereinafter, such wirings arereferred to as scan lines G_(L) _(_) ₁ to G_(L) _(_) _(X)) or a functionof supplying an initialization signal. Without being limited thereto,the gate driver circuit portions 504 a and 504 b each can control orsupply another signal.

Although the structure in which the two gate driver circuit portions 504a and 504 b are provided as gate driver circuit portions is illustratedin FIG. 5, the number of the gate driver circuit portions is not limitedthereto, and one or three or more gate driver circuit portions may beprovided.

[Source Driver Circuit Portion]

The source driver circuit portion 506 has a function of generating adata signal to be written to the pixels 10(X, Y) on the basis of animage signal, a function of controlling the potentials of wiringssupplied with data signals (such wirings are hereinafter referred to assignal lines S_(L) _(_) ₁ to S_(L) _(_) _(Y) and signal lines S_(E) _(_)₁ to S_(E) _(_) _(Y)), or a function of supplying an initializationsignal. Without being limited thereto, the source driver circuit portion506 may have a function of generating, controlling, or supplying anothersignal.

The source driver circuit portion 506 includes a plurality of analogswitches or the like. The source driver circuit portion 506 can output,as data signals, time-divided image signals obtained by sequentiallyturning on the plurality of analog switches.

Although the structure where one source driver circuit portion 506 isprovided is illustrated in FIG. 5, the number of the source drivercircuit portions is not limited thereto, and a plurality of sourcedriver circuit portions may be provided in the display device 500. Forexample, two source driver circuit portions may be provided so that thesignal lines S_(L) _(_) ₁ to S_(L) _(_) _(Y) are controlled by one ofthe source driver circuit portions and the signal lines S_(E) _(_) ₁ toS_(E) _(_) _(Y) are controlled by the other of the source driver circuitportions.

[Pixel]

A pulse signal is input to each of the pixels 10(X, Y) through one ofthe scan lines G_(L) _(_) ₁ to G_(L) _(_) _(X) and the scan lines G_(E)_(_) ₁ to G_(E) _(_) _(X). A data signal is input to each of the pixels10(X, Y) through one of the signal lines S_(L) _(_) ₁ to S_(L) _(_) _(Y)and the signal lines S_(E) _(_) ₁ to S_(E) _(_) _(Y).

For example, the pixel 10(m, n) in the m-th row and the n-th column (mis a natural number of X or less, and n is a natural number of Y orless) is supplied with pulse signals from the gate driver circuitportion 504 a through the scan lines G_(L) _(_) _(m) and G_(E) _(_) _(m)and supplied with a data signal from the source driver circuit portion506 through the signal lines S_(L) _(_) _(n) and S_(E) _(_) _(n) inaccordance with the potentials of the scan lines G_(L) _(_) _(m) andG_(E) _(_) _(m).

The pixels 10(m, n) includes two display elements as described above.The scan lines G_(L) _(_) ₁ to G_(L) _(_) _(X) are wirings which controlthe potential of a pulse signal supplied to one of the two displayelements. The scan lines G_(E) _(_) ₁ to G_(E) _(_) _(X) are wiringswhich control the potential of a pulse signal supplied to the other ofthe two display elements.

The signal lines S_(L) _(_) ₁ to S_(L) _(_) _(Y) are wirings whichcontrol the potential of a data signal supplied to one of the twodisplay elements. The signal lines S_(E) _(_) ₁ to S_(E) _(_) _(Y) arewirings which control the potential of a data signal supplied to theother of the two display elements.

[External Circuit]

External circuits 508 a and 508 b are connected to the display device500. Note that the external circuits 508 a and 508 b may be formed inthe display device 500.

As shown in FIG. 5, the external circuit 508 a is electrically connectedto wirings supplied with anode potentials (hereinafter referred to asanode lines ANO_ ₁ to ANO_ _(X) ) and the external circuit 508 b iselectrically connected to wirings supplied with common potentials(hereinafter referred to as common lines COM_ ₁ to COM_ _(X) ).

<1-2. Circuit Configuration of Pixels>

Next, the circuit configuration of the pixels 10(m, n) are describedwith reference to FIG. 6.

FIG. 6 is a circuit diagram showing the pixel 10(m, n) and an adjacentpixel 10(m, n+1) in a column direction of the pixel 10(m, n) which areincluded in the display device 500 of one embodiment of the presentinvention. In this specification and the like, the column direction is adirection in which the value of n of the signal line S_(L) _(_) _(n) (orthe signal line S_(E) _(_) _(n)) increases and decreases and the rowdirection is a direction in which the value of m of the scan line G_(L)_(_) _(m) (or the scan line G_(E) _(_) _(m)) increases and decreases.

The pixel 10(m, n) includes a transistor Tr1, a transistor Tr2, atransistor Tr3, a capacitor C1, a capacitor C2, a display element 11,and a display element 12. The pixel 10(m, n+1) has a similar structure.Note that in this specification and the like, the display element 11 iscalled a first display element and the display element 12 is called asecond display element in some cases.

The pixel 10(m, n) is electrically connected to the signal line S_(L)_(_) _(n), the signal line S_(E) _(_) _(n), the scan line G_(L) _(_)_(m), the scan line G_(E) _(_) _(m), a common line COM_ _(m) , a commonline VCOM1, a common line VCOM2, and an anode line ANO_ _(m) . The pixel10(m, n+1) is electrically connected to a signal line S_(L) _(_) _(n+1),a signal line S_(E) _(_) _(n+1), the scan line G_(L) _(_) _(m), the scanline G_(E) _(_) _(m), the common line COM_ _(m) , the common line VCOM1,the common line VCOM2, and an anode line ANO_ _(m) .

Each of the signal lines S_(L) _(_) _(n) and S_(L) _(_) _(n+1), the scanline G_(L) _(_) _(m), the common line COM_ _(m) , and the common lineVCOM1 is a wiring for driving the display element 11. Each of the signallines S_(E) _(_) _(n) and S_(E) _(_) _(n+1), the scan line G_(E) _(_)_(m), the common line VCOM2, and the anode line ANO_ _(m) is a wiringfor driving the display element 12.

In the case where a potential supplied to the signal line S_(E) _(_)_(n) and the signal line S_(E) _(_) _(n+1) is different from a potentialsupplied to the signal line S_(L) _(_) _(n) and the signal line S_(L)_(_) _(n+1), the signal line S_(E) _(_) _(n) and the signal line S_(L)_(_) _(n+1) are preferably positioned apart from each other as shown inFIG. 6. In other words, the signal line S_(E) _(_) _(n) is preferablypositioned adjacent to the signal line S_(E) _(_) _(n+1). With thisarrangement, an influence of the potential difference between the signallines S_(L) _(_) _(n) and S_(L) _(_) _(n+1) and signal lines S_(E) _(_)_(n) and S_(E) _(_) _(n+1) can be reduced.

<1-3. Structure Example of First Display Element>

The display element 11 has a function of controlling transmission orreflection of light. In particular, the display element 11 is preferablya reflective display element which controls reflection of light. Thedisplay element 11 serving as a reflective display element can reducepower consumption of the display device because display can be performedwith the use of external light. For example, the display element 11 mayhave a combined structure of a reflective film, a liquid crystalelement, and a polarizing plate or a structure using a micro electromechanical systems (MEMS).

<1-4. Structure Example of Second Display Element>

The display element 12 has a function of emitting light. Therefore, thedisplay element 12 may be rephrased as a light-emitting element. Forexample, an electroluminescent element (also referred to as an ELelement), or a light-emitting diode may be used as the display element12.

As described above, in the display device of one embodiment of thepresent invention, display elements with different functions like thedisplay elements 11 and 12 are used. In the case where a reflectiveliquid crystal element is used as one of the display elements and atransmissive EL element is used as the other of the display elements, anovel display device that is highly convenient or reliable can beprovided. Furthermore, a display device with low power consumption andhigh display quality can be provided when a reflective liquid crystalelement is used in an environment with bright external light and atransmissive EL element is used in an environment with weak externallight.

<1-5. Driving Method for Display Element>

Next, a method for driving the display element 11 and the displayelement 12 is described. Note that a structure including a liquidcrystal element as the display element 11 and a light-emitting elementas the display element 12 is used in the description below.

[Driving Method of First Display Element]

In the pixel 10(m, n), a gate electrode of the transistor Tr1 iselectrically connected to the scan line G_(L) _(_) _(m). One of a sourceelectrode and a drain electrode of the transistor Tr1 is electricallyconnected to the signal line S_(L) _(_) _(n), and the other iselectrically connected to one of a pair of electrodes of the displayelement 11. The transistor Tr1 has a function of controlling whether towrite a data signal by being turned on or off

The other of the pair of electrodes of the display element 11 iselectrically connected to the common line VCOM1.

One of a pair of electrodes of the capacitor C1 is electricallyconnected to the common line COM_ _(m) , and the other of the pair ofelectrodes of the capacitor C1 is electrically connected to the other ofthe source electrode and the drain electrode of the transistor Tr1 andthe one of the pair of electrodes of the display element 11. Thecapacitor C1 has a function of storing data written to the pixel 10(m,n).

For example, the gate driver circuit portion 504 b in FIG. 5sequentially selects the pixels 10(m, n) row by row to turn on thetransistor Tr1, and data of data signals are written. When thetransistor Tr1 is turned off, the pixel 10(m, n) to which the data hasbeen written is brought into a holding state. This operation issequentially performed row by row; thus, an image is displayed.

[Driving Method for Second Display Element]

A gate electrode of the transistor Tr2 is electrically connected to thescan line G_(E) _(_) _(m) in the pixel 10(m, n). One of a sourceelectrode and a drain electrode of the transistor Tr2 is electricallyconnected to the signal line S_(E) _(_) _(n) and the other of the sourceelectrode and the drain electrode is electrically connected to a gateelectrode of the transistor Tr3. The transistor Tr2 is configured to beturned on or off to control whether a data signal is written.

One of a pair of electrodes of the capacitor C2 is electricallyconnected to the anode line ANO_ _(m) . The other of the pair ofelectrodes of the capacitor C2 is electrically connected to the other ofthe source electrode and the drain electrode of the transistor Tr2. Thecapacitor C2 has a function of storing data written to the pixel 10(m,n).

The gate electrode of the transistor Tr3 is electrically connected tothe other of the source electrode and the drain electrode of thetransistor Tr2. One of a source electrode and a drain electrode of thetransistor Tr3 is electrically connected to the anode line ANO_ _(m) .The other of the source electrode and the drain electrode of thetransistor Tr3 is electrically connected to one of a pair of electrodesof the display element 12. The transistor Tr3 includes a backgateelectrode. The backgate electrode is electrically connected to the gateelectrode of the transistor Tr3.

The other of the pair of electrodes of the display element 12 iselectrically connected to the common line VCOM2.

For example, the gate driver circuit portion 504 a in FIG. 5sequentially selects the pixels 10(m, n) row by row to turn on thetransistors Tr2, and data of data signals are written. When thetransistor Tr2 is turned off, the pixel 10(m, n) to which the data hasbeen written is brought into a holding state. Furthermore, the amount ofcurrent flowing between the source electrode and the drain electrode ofthe transistor Tr3 is controlled in accordance with the potential of thewritten data signal. The display element 12 emits light with a luminancecorresponding to the amount of flowing current. This operation issequentially performed row by row; thus, an image is displayed.

In this manner, two display elements can be controlled separately withthe use of different transistors in the display device of one embodimentof the present invention. Accordingly, a display device having highdisplay quality can be provided.

Transistors used in the display device of one embodiment of the presentinvention (the transistors Tr1, Tr2, and Tr3) each include an oxidesemiconductor film. The transistor including an oxide semiconductor filmcan have relatively high field-effect mobility and thus can operate athigh speed. The off-state current of the transistor including an oxidesemiconductor film is extremely low. Therefore, the luminance of thedisplay device can be kept even when the refresh rate of the displaydevice is lowered, so that power consumption can be lowered.

A progressive type display, an interlace type display, or the like canbe employed as the display type of the display element 11 and thedisplay element 12. Further, as color elements controlled in the pixelat the time of color display, three colors of R (red), G (green), and B(blue) can be given. Note that color elements are not limited to thethree colors of R, G, and B. For example, one or more colors of yellow,cyan, magenta, white, and the like may be added to RGB. Further, thesizes of display regions may be different between respective dots ofcolor elements. However, the display device of one embodiment of thepresent invention is not limited to a color display device and can beapplied to a monochrome display device.

<1-6. Display Region of Display Element>

Here, the display regions of the display elements 11 and 12 in the pixel10(m, n) are described with reference to FIG. 1.

FIG. 1 is a schematic view illustrating display regions of the pixel10(m, n) and pixels 10(m, n−1) and 10(m, n+1) which are adjacent to thepixel 10(m, n) in the column direction. FIG. 1 illustrates a pixel10(m+1, n−1), a pixel 10(m+1, n), a pixel 10(m+1, n+1), and the likepositioned near the pixel 10(m, n). Note that in this specification andthe like, the pixel 10(m, n) is called a first pixel and the pixel 10(m,n+1) is called a second pixel in some cases.

The pixel 10(m, n) illustrated in FIG. 1 includes a display region 11d(m, n) that functions as a display region of the display element 11 anda display region 12 d(m, n) that functions as a display region of thedisplay element 12. The pixel 10(m, n+1) illustrated in FIG. 1 includesa display region 11 d(m, n+1) that functions as a display region of thedisplay element 11 and a display region 12 d(m, n+1) that functions as adisplay region of the display element 12.

In the following description, the display region 11 d(m, n) and thedisplay region 11 d(m, n+1) are described as display regions 11 d insome cases when they are not distinguished. Similarly, the displayregion 12 d(m, n) and the display region 12 d(m, n+1) are described asdisplay regions 12 d in some cases. In this specification and the like,the display region 11 d is called a first display region and the displayregion 12 d is called a second display region in some cases.

For example, the display region 11 d has a function of reflectingincident light and the display region 12 d has a function of emittinglight. The display region 12 d is provided inside the display region 11d. The display element 11 is provided to overlap with the display region11 d and the display element 12 is provided to overlap with the displayregion 12 d.

The area of the display region 12 d is preferably smaller than that ofthe display region 11 d, in which case power consumption of the displaydevice can be reduced. For example, in an environment with brightexternal light, the display element 11 reflects incident light anddisplays an image in the display region 11 d, and in an environment withdark external light, the display element 12 emits light and displays animage in the display region 12 d. With this structure, a display devicewith low power consumption and high display quality can be provided.

Here, the position where the display region 12 d is provided isdescribed below.

For example, in the case where an EL element is used as the displayelement 12 disposed to overlap with the display region 12 d, as methodsfor forming the EL element, two methods are given: a color filter methodin which the same EL element is used for pixels and emission colors ofthe pixels are changed with use of color films (color filters); and aseparate coloring method in which EL elements for the respective pixelsare separately formed to have different emission colors. In order toimprove the color purity, a separate coloring method and a color filtermethod may be combined.

In the case of a separate coloring method, an EL element needs to beformed for each pixel, and high accuracy for forming (aligning) anopening in a desired position in a shadow mask (also referred to as afine metal mask) is required. When a display device has high pixeldensity (i.e., high resolution), the alignment accuracy needs to behigh, which decreases the manufacturing yield of the display device.

In the display device of one embodiment of the present invention,however, the positions of the display regions 12 d in adjacent pixelsare different as illustrated in FIG. 1. With such a structure, themanufacturing yield in the case where the display elements 12 areseparately formed can be increased.

In FIG. 1, the distance between the display region 12 d(m, n) and thedisplay region 12 d(m, n+1) is indicated as a distance d₁. The distanced₁ is greater than or equal to 20 μm, preferably greater than or equalto 25 μm, more preferably greater than or equal to 30 μm, in which casethe manufacturing yield of the display device can be increased. Notethat in the case where the distance d₁ is less than 20 μm, themanufacturing yield of the display device is decreased.

FIG. 2 illustrates an example in which positions of the second displayregions 12 d in adjacent pixels are the same. In FIG. 2, a distancebetween the display region 12 d(m, n) and the display region 12 d(m,n+1) is indicated as a distance dz.

When the distance d₁ in FIG. 1 and the distance d₂ in FIG. 2 arecompared, a relation d₁>d₂ is established. Thus, the distance in thecase where the positions of the display regions 12 d in adjacent pixelsare different can be larger than that in the case where the positions ofthe display regions 12 d in adjacent pixels are the same byapproximately 10% or more.

In the display device of one embodiment of the present invention, thearea of the display region 12 d is smaller than that of the displayregion 11 d. Accordingly, in the case where EL elements are formed by aseparate coloring method, the opening in the shadow mask can be small.Thus, the mechanical strength of the shadow mask can be increased. Theshadow mask with high mechanical strength is less likely to be deformeddue to, for example, bending, distortion, expansion, or contraction,increasing the manufacturing yield.

With the arrangement of the display regions 12 d in FIG. 1, aninterference of light emitted from adjacent display elements 12 can besuppressed.

Note that FIG. 1 illustrates an example in which the display region 12 dhas a rectangular shape, but one embodiment of the present invention isnot limited thereto. The display region 12 d can have a non-rectangularshape. FIG. 3 illustrates an example in which the display region 12 dhas a non-rectangular shape.

FIG. 3 is a schematic view illustrating an example of pixel arrangement.The display region 12 d in FIG. 3 has a circular shape. In FIG. 3, adistance between the display region 12 d(m, n) and the display region 12d(m, n+1) is indicated as a distance d3. When the length of a side ofthe rectangular display region 12 d is equal to the diameter of thecircular display region 12 d, the circular display region 12 d ispreferred because the distance d3 can be longer than the distance d₁ inFIG. 1.

As described above, the display region 12 d can have various shapes (forexample, polygonal shapes such as a triangle and a rectangle, circularshapes such as a circle and an ellipse, and a combination of a polygonalshape and a circular shape).

In FIG. 1, the pixel 10(m, n−1), the pixel 10(m, n), and the pixel 10(m,n+1) are arranged in stripes in the column direction, but one embodimentof the present invention is not limited thereto. For example, astructure illustrated in FIG. 4 may be employed.

FIG. 4 is a schematic view of a display region including the pixel 10(m,n) and the pixel 10(m, n−1) and the pixel 10(m, n+1) which are adjacentto the pixel 10(m, n) in the column direction. In FIG. 4, pixels nearthe pixel 10(m, n) such as the pixel 10(m+1, n−1), a pixel 10(m′, n),the pixel 10(m+1, n), a pixel 10(m′+1, n), and the pixel 10(m+1, n+1)are illustrated.

In the structure in FIG. 4, the display region 11 d(m, n) and thedisplay region 11 d(m, n+1) have different areas. In this way, the areasof the display regions 11 d in adjacent pixels may be different. Thisapplies to the display regions 12 d which are not illustrated.

When the structure of FIG. 4 is employed, the pixel 10(m, n+1) in FIG. 1is disposed in the position of the pixel 10(m′, n) in FIG. 4.

Note that in FIG. 4, a distance between the pixel 10(m, n) and the pixel10(m, n+1) is indicated as a distance d₄, and a distance between thepixel 10(m, n) and the pixel 10(m′, n) is indicated as a distance d₅.The distance d₄ and the distance d₅ preferably have the same length, inother words, the display regions 12 d are preferably provided at equalintervals. With such a structure, openings in the shadow mask can beequally spaced, which increases the mechanical strength of the shadowmask and thus distortion of the shadow mask at evaporation can besuppressed.

As illustrated in FIG. 4, the positions of the display regions 12 d inthe pixel 10(m, n+1) adjacent to the pixel 10(m, n) in the columndirection and in the pixel 10(m′, n) are different from the position ofthe display region 12 d in the pixel 10(m, n). In other words, the pixel10(m, n) and the pixel 10(m, n+1) are provided adjacent to each other,and the display region 12 d(m, n) included in the pixel 10(m, n) and thedisplay region 12 d(m, n+1) included in the pixel 10(m, n+1) areprovided in different portions inside the respective display regions 11d.

With the arrangement of the display regions 12 d as illustrated in FIG.4, the manufacturing yield in the case where the display elements 12 areseparately formed can be increased. In addition, with the arrangement ofthe display regions 12 d as illustrated in FIG. 4, an interference oflight emitted from adjacent display elements 12 can be suppressed.

Although not illustrated, one embodiment of the present invention can beapplied to pixels in delta arrangement or pentile arrangement.

<1-7. Structure Example of Display Device (Top View)>

Next, a specific structure example of the display device 500 illustratedin FIG. 5 is described with reference to FIGS. 7A and 7B and FIG. 8.

FIG. 7A is a top view of the display device 500. As described above, thedisplay device 500 includes the pixel portion 502, the gate drivercircuit portions 504 a and 504 b and the source driver circuit portion506 placed outside the pixel portion 502. FIG. 7A schematicallyillustrates the pixel 10(m, n) included in the pixel portion 502. Aflexible printed circuit (FPC) is electrically connected to the displaydevice 500 in FIG. 7A.

FIG. 7B is a top view schematically illustrating the pixel 10(m, n)shown in FIG. 7A and the pixel 10(m, n+1) adjacent to the pixel 10(m,n). The signal lines S_(L) _(_) _(n), S_(L) _(_) _(n+1), S_(E) _(_)_(n), and S_(E) _(_) _(n+1), the scan lines G_(L) _(_) _(m) and G_(E)_(_) _(n), the common line COM_ _(m) , and the transistors Tr1, Tr2, andTr3 in FIG. 7B respectively correspond to the reference numerals in FIG.6. The display region 11 d and the display region 12 d in FIG. 7Bcorrespond to the reference numerals in FIG. 1. A common line COM__(m+1) in FIG. 7B indicates a common line included in the pixel 10(m+1,n) adjacent to the pixel 10(m, n).

<1-8. Structure Example of Display Device (Cross Section)>

Next, a cross-sectional structure of the display device 500 is describedwith reference to FIG. 8.

FIG. 8 is a cross-sectional view corresponding to cross sections takenalong the dashed-dotted lines A1-A2, A3-A4, A5-A6, A7-A8, A9-A10, andA11-A12 illustrated in FIGS. 7A and 7B.

A cross section taken along the dashed-dotted line A1-A2 corresponds toa region in which the FPC is attached to the display device 500. A crosssection taken along the dashed-dotted line A3-A4 corresponds to a regionin which the gate driver circuit portion 504 a is provided. A crosssection taken along the dashed-dotted line A5-A6 corresponds to a regionin which the display element 11 and the display element 12 are provided.A cross section taken along the dashed-dotted line A7-A8 corresponds toa region in which the display element 11 is provided. A cross sectiontaken along the dashed-dotted line A9-A10 corresponds to a connectionregion of the display device 500. A cross section taken along thedashed-dotted line A11-A12 corresponds to the edge of the display device500 and the vicinity thereof

In FIG. 8, the display device 500 includes the display element 11, thedisplay element 12, the transistor Tr1, the transistor Tr3, and atransistor Tr4 between a substrate 452 and a substrate 652. A functionalfilm 626 is provided over the substrate 652.

As described above, the display element 11 has a function of reflectingincident light and the display element 12 has a function of emittinglight. In FIG. 8, the light entering the display element 11 and thereflected light are schematically denoted by arrows of dashed lines.Furthermore, the light emitted from the display element 12 isschematically denoted by an arrow of a dashed double-dotted line.

[Cross Section of Pixel]

The cross sections taken along the dashed-dotted lines A5-A6 and A7-A8in FIG. 8 are described with reference to FIG. 9. FIG. 9 corresponds toan enlarged cross-sectional view of some components taken along thedashed-dotted lines A5-A6 and A7-A8 in FIG. 8. The enlargedcross-sectional view is reversed upside down. Note that in FIG. 9, somecomponents are not illustrated in order to avoid complexity of thedrawing.

The display element 11 includes a conductive film 403 b, a liquidcrystal layer 620, and a conductive film 608. The conductive film 403 bfunctions as a pixel electrode and the conductive film 608 functions asa counter electrode. The conductive film 403 b is electrically connectedto the transistor Tr1.

The display element 11 includes conductive films 405 b and 405 celectrically connected to the conductive film 403 b. The conductivefilms 405 b and 405 c each have a function of reflecting incident light.That is, the conductive films 405 b and 405 c function as reflectivefilms. An opening 450 transmitting incident light is provided in thereflective films. In FIG. 9, a conductive film functioning as areflective film is separated into island shapes by the opening 450,whereby the conductive film 405 c is positioned below the transistor Tr1and the conductive film 405 b is positioned below the transistor Tr3.Since light of the display element 12 is emitted from the opening 450,the opening 450 corresponds to the display region 12 d(m, n) illustratedin FIG. 8.

The display element 12 has a function of emitting light toward theopening 450. In FIG. 9, the display element 12 is a bottom emission typelight-emitting element.

The display element 12 includes a conductive film 417, an EL layer 419,and a conductive film 420. The conductive film 417 functions as a pixelelectrode and an anode electrode. The conductive film 420 functions as acounter electrode and a cathode electrode. Although a description ismade on a structure where the conductive film 417 functions as an anodeelectrode and the conductive film 420 functions as a cathode electrodein this embodiment, one embodiment of the present invention is notlimited thereto. For example, the conductive film 417 may function as acathode electrode and the conductive film 420 may function as an anodeelectrode.

The conductive film 417 is electrically connected to the transistor Tr3.

Each of the transistor Tr1 and the transistor Tr3 preferably has astaggered structure (also referred to as a top gate structure) asillustrated in FIG. 9. When the staggered structure is employed,parasitic capacitance that can be generated between a gate electrode anda source electrode and between the gate electrode and a drain electrodecan be reduced. However, one embodiment of the present invention is notlimited to this, and a transistor having an inverted staggered structure(also referred to as a bottom gate structure) may be used.

The transistor Tr1 is formed over an insulating film 406 and aninsulating film 408 and includes an oxide semiconductor film 409 c overthe insulating film 408, an insulating film 410 c over the oxidesemiconductor film 409 c, and an oxide semiconductor film 411 c over theinsulating film 410 c. The insulating film 410 c functions as a gateinsulating film and the oxide semiconductor film 411 c functions as agate electrode.

Insulating films 412 and 413 are provided over the oxide semiconductorfilms 409 c and 411 c. An opening reaching the oxide semiconductor film409 c is provided in the insulating films 412 and 413 and conductivefilms 414 f and 414 g are electrically connected to the oxidesemiconductor film 409 c through the opening. The conductive films 414 fand 414 g function as a source electrode and a drain electrode of thetransistor Tr1.

Insulating films 416 and 418 are provided over the transistor Tr1.

The transistor Tr3 is formed over the insulating film 406, and includesa conductive film 407 b over the insulating film 406, the insulatingfilm 408 over the conductive film 407 b, an oxide semiconductor film 409b over the insulating film 408, an insulating film 410 b over the oxidesemiconductor film 409 b, and an oxide semiconductor film 411 b over theinsulating film 410 b. The conductive film 407 b functions as a firstgate electrode, and the insulating film 408 functions as a first gateinsulating film. The insulating film 410 b functions as a second gateinsulating film, and the oxide semiconductor film 411 b functions as asecond gate electrode.

Insulating films 412 and 413 are provided over the oxide semiconductorfilms 409 b and 411 b. An opening reaching the oxide semiconductor film409 b is provided in the insulating films 412 and 413 and conductivefilms 414 d and 414 e are electrically connected to the oxidesemiconductor film 409 b through the opening. The conductive films 414 dand 414 e function as a source electrode and a drain electrode of thetransistor Tr3.

A conductive film 414 e is electrically connected to a conductive film407 f through an opening provided in the insulating films 406, 408, 412,and 413. The conductive film 407 f is formed through the same process asthat of the conductive film 407 b and functions as a connectionelectrode.

The insulating film 416 and the conductive film 417 are provided overthe transistor Tr3. An opening reaching the conductive film 414 d isprovided in the insulating film 416, and the conductive film 414 d andthe conductive film 417 are electrically connected to each other throughthe opening.

An insulating film 418, the EL layer 419, and the conductive film 420are provided over the conductive film 417. An opening reaching theconductive film 417 is provided in the insulating film 418, and theconductive film 417 and the EL layer 419 are electrically connected toeach other through the opening.

The conductive film 420 is adhered to the substrate 452 with a sealingmaterial 454 placed therebetween.

A color film 604, an insulating film 606, and the conductive film 608are provided over the substrate 652 that faces the substrate 452. Afunctional film 626 is provided below the substrate 652. Light reflectedby the display element 11 and light emitted from the display element 12are extracted through the color film 604, the functional film 626, andthe like.

The display element 11 includes alignment films 618 a and 618 b incontact with the liquid crystal layer 620 as illustrated in FIG. 9. Notethat a structure without the alignment films 618 a and 618 b may beemployed.

When the transistors Tr1 and Tr3 have top-gate structures as illustratedin FIG. 9, the area of the circuit can be reduced. The transistor Tr1 isa single-gate transistor in which the oxide semiconductor film 411 cfunctioning as a gate electrode is provided, whereas the transistor Tr3is a multi-gate transistor in which the conductive film 407 bfunctioning as a first gate electrode and the oxide semiconductor film411 b functioning as a second gate electrode are provided. Note thatthere is no limitation on the structure of the transistor that is usedin the display device of one embodiment of the present invention. Forexample, both the transistors Tr1 and Tr3 may have either a single-gatestructure or a multi-gate structure.

[Cross Sections of FPC Region and Gate Driver Circuit Portion]

The cross-sections taken along the dashed-dotted lines A1-A2 and A3-A4in FIG. 8 are described with reference to FIG. 10. FIG. 10 correspondsto an enlarged cross-sectional view of components taken along thedashed-dotted lines A1-A2 and A3-A4 in FIG. 8. The enlargedcross-sectional view is reversed upside down. Note that in FIG. 10, somecomponents are not illustrated in order to avoid complexity of thedrawing.

The FPC illustrated in FIG. 10 is electrically connected to a conductivefilm 403 a through an anisotropic conductive film (ACF). An insulatingfilm 404 is provided over the conductive film 403 a. An opening reachingthe conductive film 403 a is provided in the insulating film 404, andthe conductive film 403 a and a conductive film 405 a are electricallyconnected to each other through the opening.

The insulating film 406 is provided over the conductive film 405 a. Anopening reaching the conductive film 405 a is provided in the insulatingfilm 406, and the conductive film 405 a and a conductive film 407 a areelectrically connected to each other through the opening. The insulatingfilms 408, 412, and 413 are provided over the conductive film 407 a. Anopening reaching the conductive film 407 a is provided in the insulatingfilms 408, 412, and 413 and the conductive film 407 a and a conductivefilm 414 a are electrically connected to each other through the opening.

The insulating films 416 and 418 are provided over the insulating film413 and the conductive film 414 a. The insulating film 418 is adhered tothe substrate 452 with the sealing material 454 placed therebetween.

The transistor Tr4 illustrated in FIG. 10 corresponds to a transistorincluded in a gate driver circuit portion 504 a.

The transistor Tr4 is formed over the insulating film 406 and includes aconductive film 407 e over the insulating film 406, the insulating film408 over the conductive film 407 e, an oxide semiconductor film 409 aover the insulating film 408, an insulating film 410 a over the oxidesemiconductor film 409 a, and an oxide semiconductor film 411 a over theinsulating film 410 a. The conductive film 407 e functions as a firstgate electrode. The insulating film 410 a functions as a second gateinsulating film and the oxide semiconductor film 411 a functions as asecond gate electrode.

The insulating films 412 and 413 are provided over the oxidesemiconductor films 409 a and 411 a. An opening reaching the oxidesemiconductor film 409 a is provided in the insulating films 412 and 413and conductive films 414 b and 414 c are electrically connected to theoxide semiconductor film 409 a through the opening. The conductive films414 b and 414 c function as a source electrode and a drain electrode ofthe transistor Tr4.

The transistor Tr4 is a multi-gate transistor like the transistor Tr3described above. A multi-gate transistor is preferably used in the gatedriver circuit portion 504 a because the current drive capability can beimproved. Since the use of a multi-gate transistor can improve thecurrent drive capability, the width of the driver circuit can bereduced.

The insulating films 416 and 418 are provided over the transistor Tr4.The insulating film 418 is adhered to the substrate 452 with the sealingmaterial 454 placed therebetween.

A light-blocking film 602, the insulating film 606, and the conductivefilm 608 are provided over the substrate 652 that faces the substrate452.

A structure body 610 a is formed in a position overlapping with thetransistor Tr4 over the conductive film 608. The structure body 610 ahas a function of controlling the thickness of the liquid crystal layer620. The alignment films 618 a and 618 b are formed between thestructure body 610 a and the insulating film 404 in FIG. 10. Note thatthe alignment films 618 a and 618 b are not necessarily formed betweenthe structure body 610 a and the insulating film 404.

A sealant 622 is provided at an end portion of the substrate 652. Notethat the sealant 622 is provided between the substrate 652 and theconductive film 403 a.

[Cross Sections of Connection Region and Region in the Vicinity of EndPortion]

The cross sections taken along the dashed-dotted lines A9-A10 andA11-A12 in

FIG. 8 are described with reference to FIG. 11. FIG. 11 corresponds toan enlarged cross-sectional view of components taken along thedashed-dotted lines A9-A10 and A11-A12 in FIG. 8. The enlargedcross-sectional view is reversed upside down. Note that in FIG. 11, somecomponents are not illustrated in order to avoid complexity of thedrawing.

In FIG. 11, the conductive film 608 is electrically connected to aconductive film 403 c through a conductor 624. The conductor 624 isincluded in the sealant 622. The conductive film 608 is provided overthe substrate 652, the light-blocking film 602, and the insulating film606.

The insulating film 404 is provided over the conductive film 403 c. Anopening reaching the conductive film 403 c is provided in the insulatingfilm 404, and the conductive film 403 c and a conductive film 405 d areelectrically connected to each other through the opening. The insulatingfilm 406 is provided over the conductive film 405 d. An opening reachingthe conductive film 405 d is provided in the insulating film 406, andthe conductive film 405 d and a conductive film 407 d are electricallyconnected to each other through the opening.

The insulating films 408, 412, and 413 are provided over the conductivefilm 407 d. An opening reaching the conductive film 407 d is provided inthe insulating films 408, 412, and 413 and the conductive film 407 d anda conductive film 414 h are electrically connected to each other throughthe opening. The insulating films 416 and 418 are provided over theconductive film 414 h. The insulating film 418 is adhered to thesubstrate 452 with the sealing material 454 placed therebetween.

The sealant 622 is provided at end portions of the substrate 452 and652. Note that the sealant 622 is provided between the substrate 652 andthe insulating film 404.

<1-9. Manufacturing Method of Display Device>

Next, a method for manufacturing the display device 500 illustrated inFIG. 8 is described with reference to FIGS. 12A to 12C, FIGS. 13A to13C, FIGS. 14A to 14C, FIGS. 15A to 15C, FIGS. 16A and 16B, and FIG. 17.FIGS. 12A to 12C to FIG. 17 are cross-sectional views illustrating amethod for manufacturing the display device 500.

First, a conductive film 402 is formed over a substrate 401. Then, aconductive film is formed over the conductive film 402 and processedinto island shapes, whereby the conductive films 403 a, 403 b, and 403 care formed (see FIG. 12A).

The conductive film 402 has a function of a separation layer, theconductive films 403 a and 403 c each have a function of a connectionelectrode, and the conductive film 403 b has a function of a pixelelectrode.

An insulating film is formed over the conductive films 402, 403 a, 403b, and 403 c and openings are formed in desired regions of theinsulating film, whereby the insulating film 404 is formed. Then, aconductive film is formed over the conductive films 403 a, 403 b, and403 c and the insulating film 404 and processed into island shapes,whereby the conductive films 405 a, 405 b, 405 c, and 405 d are formed(see FIG. 12B).

The insulating film 404 has openings in regions overlapping with theconductive films 403 a, 403 b, and 403 c. The conductive film 403 a iselectrically connected to the conductive film 405 a through the opening,the conductive film 403 b is electrically connected to the conductivefilms 405 b and 405 c through the openings, and the conductive film 403c is electrically connected to the conductive film 405 d through theopening.

An insulating film is formed over the insulating film 404 and theconductive films 405 a, 405 b, 405 c, and 405 d and openings are formedin desired regions of the insulating film, whereby the insulating film406 is formed. A conductive film is formed over the conductive films 405a, 405 b, 405 c, and 405 d and the insulating film 406 and processedinto island shapes, whereby the conductive films 407 a, 407 b, 407 c,407 d, 407 e, 407 f, and 407 g are formed (see FIG. 12C).

The insulating film 406 has openings in regions overlapping with theconductive films 405 a, 405 c, and 405 d. The conductive film 405 a, theconductive film 405 c, and the conductive film 405 d are electricallyconnected to the conductive film 407 a, the conductive film 407 c, andthe conductive film 407 d, respectively, through the openings.

Next, the insulating film 408 is formed over the insulating film 406 andthe conductive films 407 a, 407 b, 407 c, 407 d, 407 e, 407 f, and 407g. Then, an oxide semiconductor film is formed over the insulating film408 and processed into island shapes, whereby the oxide semiconductorfilms 409 a, 409 b, and 409 c are formed (see FIG. 13A).

Next, an insulating film and an oxide semiconductor film are formed overthe insulating film 408 and the oxide semiconductor films 409 a, 409 b,and 409 c and processed into desired shapes, whereby the island-shapedinsulating films 410 a, 410 b, and 410 c and the island-shaped oxidesemiconductor films 411 a, 411 b, and 411 c are formed (see FIG. 13B).

Next, insulating films are formed over the insulating film 408 and theoxide semiconductor films 409 a, 409 b, and 409 c and openings areformed in desired regions of the insulating films, whereby theinsulating films 412 and 413 are formed (see FIG. 13C).

Although a two-layer structure of the insulating films 412 and 413 isillustrated in FIG. 13C, the present invention is not limited thereto.For example, a single-layer structure of the insulating film 412, asingle-layer structure of the insulating film 413, or a stacked-layerstructure of three or more layers in which the insulating films 412 and413 and another insulating film are stacked may be used. When openingsare formed in the insulating films 412 and 413, openings are also formedin part of the insulating film 408. Openings formed in the insulatingfilms 408, 412, and 413 reach the conductive films 407 a, 407 c, 407 d,and 407 f.

Next, a conductive film is formed over the insulating film 413 andprocessed into desired shapes, whereby the conductive films 414 a, 414b, 414 c, 414 d, 414 e, 414 f, 414 g, and 414 h are formed (see FIG.14A).

The conductive films 414 b and 414 c function as a source electrode anda drain electrode of the transistor Tr4. The conductive films 414 d and414 e function as a source electrode and a drain electrode of thetransistor Tr3. The conductive films 414 f and 414 g function as asource electrode and a drain electrode of the transistor Tr1.

In the transistor Tr1, the conductive film 414 g is electricallyconnected to the conductive film 403 b with the conductive films 407 cand 405 c placed therebetween. The transistor Tr1 can control thepotential of the conductive film 403 b.

Next, the insulating film 416 is formed to cover the transistors Tr1,Tr3, and Tr4. The insulating film 416 has an opening in a regionoverlapping with the conductive film 414 d. Next, a conductive film isformed over the insulating film 416 and the conductive film 414 d andprocessed into a desired shape, whereby the conductive film 417 isformed. Then, the insulating film 418 is formed in a desired region overthe insulating film 416 and the conductive film 417. The insulating film418 has an opening in a region overlapping with the conductive film 417(see FIG. 14B).

Next, the EL layer 419 is formed over the conductive film 417 and theinsulating film 418, and the conductive film 420 is formed over the ELlayer 419 (see FIG. 14C).

The conductive film 417, the EL layer 419, and the conductive film 420forms the display element 12. Note that the conductive film 417functions as one of a pair of electrodes of the display element 12, andthe conductive film 420 functions as the other thereof. Although notillustrated, the EL layers 419 are separately formed for color elements(RGB). Note that details of the manufacturing method of the displayelement 12 are described in Embodiment 2.

Through the above steps, an element formed over the substrate 401 can befabricated.

A method for manufacturing the substrate 652 disposed to face thesubstrate 452 is described with reference to FIGS. 15A to 15C.

First, the light-blocking film 602 is formed over the substrate 652.After that, the color film 604 is formed over the substrate 652 and thelight-blocking film 602 (see FIG. 15A).

Next, the insulating film 606 is formed over the light-blocking film 602and the color film 604. Then, the conductive film 608 is formed over theinsulating film 606 (see FIG. 15B).

Next, the structure bodies 610 a and 610 b are formed in desired regionsover the conductive film 608. Then, the alignment film 618 b is formedover the conductive film 608 and the structure bodies 610 a and 610 b(see FIG. 15C).

Note that a structure without the alignment film 618 b may be employed.Although the structure bodies 610 a and 610 b are formed over thesubstrate 652 in this embodiment, the present invention is not limitedthereto. For example, the structure bodies 610 a and 610 b may be formedover the above-described element formed over the substrate 401.

Through the above steps, an element formed over the substrate 652 can befabricated.

Next, the element formed over the substrate 401 is separated from thesubstrate 401. Specifically, separation is conducted at an interfacebetween the conductive film 402 formed over the substrate 401 and theconductive films 403 a, 403 b, and 403 c and the insulating film 404which are formed over the conductive film 402. For the separation, thesealing material 454 is formed over the element formed over thesubstrate 401. Then, the substrate 452 is attached to the sealingmaterial 454 and the element is separated at the interface between theelement and the conductive film 402 (see FIG. 16A).

When the element is separated at the interface between the element andthe conductive film 402, surfaces of the conductive films 403 a, 403 b,and 403 c (bottom surfaces of the conductive films 403 a, 403 b, and 403c in FIG. 16A) are exposed. In the case where an insulating film, aforeign substance, or the like is attached to the surfaces of theconductive films 403 a, 403 b, and 403 c, the insulating film, theforeign substance, or the like is preferably removed by cleaningtreatment, ashing treatment, etching treatment, or the like.

When the element is separated at the interface between the element andthe conductive film 402, a polar solvent (typically water), a nonpolarsolvent, or the like is preferably added to the interface between theconductive film 402 and the conductive films 403 a, 403 b, and 403 c andthe insulating film 404 which are formed over the conductive film 402.For example, it is preferable to use water in separating the element atthe interface between the element and the conductive film 402 becausedamage caused by electrification in separation can be reduced.

As the conductive film 402, any of the following materials can be used.The conductive film 402 can have a single-layer structure or astacked-layer structure containing an element selected from tungsten,molybdenum, titanium, tantalum, niobium, nickel, cobalt, zirconium,zinc, ruthenium, rhodium, palladium, osmium, iridium, and silicon; analloy material containing any of the elements; or a compound materialcontaining any of the elements. In the case of a layer containingsilicon, the layer containing silicon may have an amorphous,microcrystalline, polycrystalline, or single-crystal structure.

When the conductive film 402 is formed as a stacked layer structureincluding a layer containing tungsten and a layer containing an oxide oftungsten, the layer containing tungsten may be formed and an insulatinglayer containing an oxide may be formed thereover so that the layercontaining an oxide of tungsten is formed at the interface between thetungsten layer and the insulating layer. Alternatively, the layercontaining an oxide of tungsten may be formed by performing thermaloxidation treatment, oxygen plasma treatment, dinitrogen monoxide (N20)plasma treatment, treatment with a highly oxidizing solution such asozone water, or the like on the surface of the layer containingtungsten. Plasma treatment or heat treatment may be performed in anatmosphere of oxygen, nitrogen, or dinitrogen monoxide alone, or a mixedgas of any of these gasses and another gas. The surface condition of theconductive film 402 is changed by the plasma treatment or the heattreatment, whereby adhesion between the conductive film 402 and theconductive films 403 a, 403 b, and 403 c and the insulating film 404which are formed later can be controlled.

Although the structure where the conductive film 402 is provided isdescribed in this embodiment, the present invention is not limitedthereto. For example, a structure where the conductive film 402 is notprovided may be employed. In that case, an organic resin film may beformed in a region where the conductive film 402 is formed. As theorganic resin film, for example, a polyimide resin film, a polyamideresin film, an acrylic resin film, an epoxy resin film, or a phenolresin film can be used.

In the case where the organic resin film is used instead of theconductive film 402, as a method for separating the element formed overthe substrate 401, a laser light is irradiated from the lower side ofthe substrate 401 to weaken the organic resin film, whereby separationis conducted at an interface between the substrate 401 and the organicresin film or at an interface between the organic resin film and theconductive films 403 a, 403 b, and 403 c and the insulating film 404.

In the case where a laser light is irradiated, a region having strongadhesion and a region having weak adhesion are formed between thesubstrate 401 and the conductive films 403 a, 403 b, and 403 c and theinsulating film 404 by adjustment of the irradiation energy density ofthe laser light, and then, the element may be separated from thesubstrate 401.

Next, the element is reversed so that the substrate 452 is placed at thebottom, and the alignment film 618 a is formed over the insulating film404 and the conductive film 403 b (see FIG. 16B).

Next, an element over the substrate 452 and an element over thesubstrate 652 are attached to each other and sealed with the sealant622. After that, the liquid crystal layer 620 is formed between thesubstrates 452 and 652, whereby the display element 11 is formed (seeFIG. 17).

Note that the conductor 624 is provided in the sealant 622 over theconductive film 403 c. As the conductor 624, conductive particles may bedispersed into a desired region in the sealant 622 by a dispenser methodor the like. The conductive film 403 c and the conductive film 608 areelectrically connected to each other through the conductor 624.

Next, the functional film 626 is formed over the substrate 652 (see FIG.17). Note that the functional film 626 is not necessarily formed.

After that, the FPC is bonded to the conductive film 403 a with the ACFplaced therebetween. Note that an anisotropic conductive paste (ACP) maybe used instead of the ACF.

Through the above steps, the display device 500 illustrated in FIG. 8can be fabricated.

<1-10. Modification Example 1 of Display Device>

A touch panel may be provided in the display device 500 illustrated inFIG. 8. As the touch panel, a capacitive touch panel (a surfacecapacitive touch panel or a projected capacitive touch panel) can bepreferably used.

A structure in which a touch panel is provided in the display device 500is described with reference to FIG. 18 to FIG. 20.

FIG. 18 is a cross-sectional view of a structure in which a touch panel691 is provided in the display device 500. FIG. 19 is a cross-sectionalview of a structure in which a touch panel 692 is provided in thedisplay device 500. FIG. 20 is a cross-sectional view of a structure inwhich a touch panel 693 is provided in the display device 500.

First, the touch panel 691 illustrated in FIG. 18 is described below.

The touch panel 691 illustrated in FIG. 18 is an in-cell touch panelthat is provided between the substrate 652 and the color film 604. Thetouch panel 691 is formed over the substrate 652 before thelight-blocking film 602 and the color film 604 are formed.

The touch panel 691 includes a light-blocking film 662, an insulatingfilm 663, an electrode 664, an electrode 665, an insulating film 666, anelectrode 667, and an insulating film 668. Changes in the mutualcapacitance in the electrodes 664 and 665 can be detected when an objectsuch as a finger or a stylus approaches, for example.

An intersection portion of the electrode 664 and the electrode 665 isshown above the transistor Tr4 illustrated in FIG. 18. The electrode 667is electrically connected to the two electrodes 664 between which theelectrode 665 is sandwiched through openings provided in the insulatingfilm 666. Although a region in which the electrode 667 is provided islocated in a region corresponding to the gate driver circuit portion 504a in FIG. 18, it is not limited thereto, and the region in which theelectrode 667 is provided may be located in a region where the pixel10(m, n) is provided, for example.

The electrodes 664 and 665 are provided in a region overlapping with thelight-blocking film 662. As illustrated in FIG. 18, it is preferablethat the electrode 664 do not overlap with the display element 12. Inother words, the electrode 664 has openings in regions overlapping withthe display element 12. That is, the electrode 664 has a mesh shape.With this structure, the electrode 664 does not block light emitted fromthe display element 12. Therefore, since luminance is hardly reducedeven when the touch panel 691 is provided, a display device with highvisibility and low power consumption can be obtained. Note that theelectrode 665 can have a structure similar to that of the electrode 664.

Since the electrodes 664 and 665 do not overlap with the display element12, a metal material whose transmittance of visible light is low can beused for the electrodes 664 and 665. Therefore, as compared with thecase of using an oxide material whose transmittance of visible light ishigh, resistance of the electrodes 664 and 665 can be reduced, wherebysensitivity of the sensor of the touch panel can be increased.

Next, the touch panel 692 illustrated in FIG. 19 and the touch panel 693illustrated in FIG. 20 are described below.

The touch panel 692 illustrated in FIG. 19 is an on-cell touch panelthat is provided above the substrate 652. The touch panel 692 has astructure similar to that of the touch panel 691.

The touch panel 693 illustrated in FIG. 20 is provided over a substrate672 and is bonded to the substrate 652 with a bonding material 674. Thetouch panel 693 is an out-cell touch panel (also referred to as anexternally attached touch panel). The touch panel 693 has a structuresimilar to that of the touch panel 691. The touch panel 693 furtherincludes a substrate 670, in addition to the components included in thetouch panel 691. The substrate 670 has a function of protecting thetouch panel 693. Note that the substrate 670 is not necessarilyprovided.

In this manner, the display device of one embodiment of the presentinvention can be combined with various types of touch panels.

<1-11. Modification Example 2 of Display Device>

FIG. 8 and FIG. 18 to FIG. 20 illustrate examples in which thefunctional film 626 is positioned outside the substrate 652, but oneembodiment of the present invention is not limited to these structures.For example, a structure in which the substrate 652 is not provided maybe employed, and examples of the structure without the substrate 652 areillustrated in FIG. 21 to FIG. 24.

FIG. 21 illustrates a modification example of the display device 500illustrated in FIG. 8. In FIG. 21, the substrate 652 is not provided andsealing is performed by the functional film 626. In this case, amaterial used for a circularly polarizing plate can be suitably used forthe functional film 626.

FIG. 22 illustrates a modification example of the display device 500illustrated in FIG. 18. In FIG. 22, the substrate 652 is not providedand the functional film 626 functions as part of the touch panel 691.

FIG. 23 illustrates a modification example of the display device 500illustrated in FIG. 19. In FIG. 23, the functional film 626 is providedinside the touch panel 692.

FIG. 24 illustrates a modification example of the display device 500illustrated in FIG. 20. In FIG. 24, the substrate 652 is not provided,and the functional film 626 is bonded to the touch panel 693 with thebonding material 674 interposed therebetween.

The structures as illustrated in FIG. 21 to FIG. 24 in which thesubstrate 652 is not provided are preferred because the thickness of thedisplay device 500 can be small.

<1-12. Modification Example 3 of Display Device>

An example of a structure where the liquid crystal element of thedisplay device 500 illustrated in FIG. 8 is a horizontal electric fieldmode liquid crystal element, (here, a fringe field switching (FFS) modeliquid crystal element) is shown in FIG. 25.

The display device 500 illustrated in FIG. 25 includes an insulatingfilm 681 over the conductive films 403 b and 403 c and a conductive film682 over the insulating film 681 in addition to the above-mentionedcomponents.

The insulating film 681 has an opening in a connection region takenalong the dashed-dotted line A9-A10, and the conductive film 682 iselectrically connected to the conductive film 403 c through the opening.In FIG. 25, the conductor 624 included in the sealant 622 in FIG. 8 isnot provided.

The conductive film 682 functions as a common electrode. The conductivefilm 682 may have a comb-like shape or a shape having a slit when seenfrom the above. Since the conductive film 682 is provided in the displaydevice 500 illustrated in FIG. 25, the conductive film 608 provided onthe substrate 652 side in FIG. 8 is not provided. Note that theconductive film 682 may be provided and the conductive film 608 may befurther provided on the substrate 652 side.

When the conductive film 682 is formed using a light-transmittingmaterial, a light-transmitting capacitor can be formed. Thelight-transmitting capacitor includes the conductive film 682, theinsulating film 681 overlapping with the conductive film 682, and theconductive film 403 c. This structure is preferable because the amountof charge accumulated in the capacitor can be increased.

<1-13. Components of Display Device>

Next, the components of the display device 500 and the manufacturingmethod thereof illustrated in FIG. 8 to FIG. 25 are described below.

[Substrate]

The substrates 401, 452, 652 and 670 can be formed using a materialhaving heat resistance high enough to withstand heat treatment in themanufacturing process.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass, quartz, sapphire, or the like can be used. Alternatively, aninorganic insulating film may be used. Examples of the inorganicinsulating film include a silicon oxide film, a silicon nitride film, asilicon oxynitride film, and an alumina film.

The non-alkali glass preferably has a thickness of greater than or equalto 0.2 nm and less than or equal to 0.7 mm, for example. The non-alkaliglass may be polished to obtain the above thickness.

For example, a large-sized glass substrate having any of the followingsizes can be used as each of the substrates 401, 452, 652, and 670: the6th generation (1500 mm×1850 mm), the 7th generation (1870 mm×2200 mm),the 8th generation (2200 mm×2400 mm), the 9th generation (2400 mm×2800mm), and the 10th generation (2950 mm×3400 mm). Thus, a large-sizeddisplay device can be manufactured.

Alternatively, as the substrates 401, 452, 652, and 670, asingle-crystal semiconductor substrate or a polycrystallinesemiconductor substrate made of silicon or silicon carbide, a compoundsemiconductor substrate made of silicon germanium or the like, an SOIsubstrate, or the like may be used.

Alternatively, for the substrates 401, 452, 652, and 670, an inorganicmaterial such as a metal may be used. Examples of the inorganic materialsuch as a metal include stainless steel and aluminum.

Alternatively, for the substrates 401, 452, 652, and 670, an organicmaterial such as a resin, a resin film, or plastic may be used. Examplesof the resin film include polyester, polyolefin, polyamide (e.g., nylonor aramid), polyimide, polycarbonate, polyurethane, an acrylic resin, anepoxy resin, polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyether sulfone (PES), and a resin having a siloxane bond.

Alternatively, for the substrates 401, 452, 652, and 670, a compositematerial of a combination of an inorganic material and an organicmaterial may be used. Examples of the composite material include a resinfilm to which a metal plate or a thin glass plate is bonded, a resinfilm into which a fibrous or particulate metal or a fibrous orparticulate glass is dispersed, and an inorganic material into which afibrous or particulate resin is dispersed.

[Conductive Film]

A metal film having conductivity, a conductive film having a function ofreflecting visible light, or a conductive film having a function oftransmitting visible light may be used as the conductive films 402, 403a, 403 b, 403 c, 405 a, 405 b, 405 c, 405 d, 407 a, 407 b, 407 c, 407 d,407 e, 411 a, 411 b, 411 c, 414 a, 414 b, 414 c, 414 d, 414 e, 414 f,414 g, 414 h, 417, 420, 608, and 682.

A material containing a metal element selected from aluminum, gold,platinum, silver, copper, chromium, tantalum, titanium, molybdenum,tungsten, nickel, iron, cobalt, palladium, and manganese can be used forthe metal film having conductivity. Alternatively, an alloy containingany of the above metal elements may be used.

For the metal film having conductivity, specifically a two-layerstructure in which a copper film is stacked over a titanium film, atwo-layer structure in which a copper film is stacked over a titaniumnitride film, a two-layer structure in which a copper film is stackedover a tantalum nitride film, or a three-layer structure in which atitanium film, a copper film, and a titanium film are stacked in thisorder may be used. In particular, a conductive film containing a copperelement is preferably used because the resistance can be reduced. As anexample of the conductive film containing a copper element, an alloyfilm containing copper and manganese is given. The alloy film ispreferable because it can be processed by a wet etching method.

As the metal film having conductivity, a conductive macromolecule or aconductive polymer may be used.

For the conductive film having a function of reflecting visible light, amaterial containing a metal element selected from gold, silver, copper,and palladium can be used. In particular, a conductive film containing asilver element is preferably used because reflectance of visible lightcan be improved.

For the conductive film having a function of transmitting visible light,a material containing an element selected from indium, tin, zinc,gallium, and silicon can be used. Specifically, an In oxide, a Zn oxide,an In—Sn oxide (also referred to as ITO), an In—Sn—Si oxide (alsoreferred to as ITSO), an In—Zn oxide, an In—Ga—Zn oxide, or the like canbe used.

As the conductive film having a function of transmitting visible light,a film containing graphene or graphite may be used. The film containinggraphene can be formed in the following manner: a film containinggraphene oxide is formed and is reduced. As a reducing method, a methodwith application of heat, a method using a reducing agent, or the likecan be employed.

Note that the conductive films 403 c and 417 each having a function of apixel electrode contain at least one metal element contained in theoxide semiconductor films 409 a, 409 b, and 409 c. For example, in thecase where the oxide semiconductor films 409 a, 409 b, and 409 c includea metal oxide such as an In-M-Zn oxide (M is Al, Ga, Y, or Sn), theconductive film 403 c and the conductive film 417 each contain any oneof In, M (M is Al, Ga, Y, or Sn), and Zn.

[Insulating Film]

For the insulating films 404, 406, 408, 410 a, 410 b, 410 c, 412, 413,416, 418, 606, 663, 666, 668, and 681, an inorganic insulating material,an organic insulating material, or an insulating composite materialincluding an insulating inorganic material and an insulating organicmaterial can be used.

Examples of the insulating inorganic material include a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film, a siliconnitride oxide film, and an aluminum oxide film. Alternatively, aplurality of the above inorganic materials may be stacked.

As the above insulating organic material, for example, materials thatinclude polyester, polyolefin, polyamide (e.g., nylon or aramid),polyimide, polycarbonate, polyurethane, an acrylic resin, an epoxyresin, or a resin having a siloxane bond can be used. As the insulatingorganic material, a photosensitive material may be used.

[Oxide Semiconductor Film]

The oxide semiconductor films 409 a, 409 b, and 409 c are formed using ametal oxide such as an In-M-Zn oxide (M is Al, Ga, Y, or Sn).Alternatively, an In—Ga oxide or an In—Zn oxide may be used for theoxide semiconductor films 409 a, 409 b, and 409 c.

In the case where the oxide semiconductor films 409 a, 409 b, and 409 cinclude an In-M-Zn oxide, the proportions of In and M, the summation ofwhich is assumed to be 100 atomic %, are as follows: the proportion ofIn is higher than 25 atomic % and the proportion of M is lower than 75atomic %, or the proportion of In is higher than 34 atomic % and theproportion of M is lower than 66 atomic %.

The energy gap of the oxide semiconductor films 409 a, 409 b, and 409 cis preferably 2 eV or more, 2.5 eV or more, or 3 eV or more.

The thickness of each of the oxide semiconductor films 409 a, 409 b, and409 c is greater than or equal to 3 nm and less than or equal to 200 nm,preferably greater than or equal to 3 nm and less than or equal to 100nm, further preferably greater than or equal to 3 nm and less than orequal to 60 nm.

In the case where the oxide semiconductor films 409 a, 409 b, and 409 cinclude an In-M-Zn oxide, the atomic ratio of metal elements in asputtering target used for depositing the In-M-Zn oxide preferablysatisfies In≧M and Zn≧M. As the atomic ratio of metal elements in such asputtering target, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=2:1:1.5,In:M:Zn=2:1:2.3, In:M:Zn=2:1:3, In:M:Zn=3:1:2, In:M:Zn=4:2:4.1,In:M:Zn=5:1:7, or the like is preferable. Note that the atomic ratio ofmetal elements in the deposited oxide semiconductor films 409 a, 409 b,and 409 c may vary from the above atomic ratio of metal elements in thesputtering target within a range of approximately ±40%. For example,when a sputtering target whose atomic ratio of In to Ga and Zn is4:2:4.1 is used, the atomic ratio of In to Ga and Zn in the depositedoxide semiconductor film may be approximately 4:2:3. In the case where asputtering target whose atomic ratio of In to Ga and Zn is 5:1:7 isused, the atomic ratio of In to Ga and Zn in the deposited oxidesemiconductor film may be approximately 5:1:6.

When silicon or carbon, which are elements belonging to Group 14, iscontained in the oxide semiconductor films 409 a, 409 b, and 409 c,oxygen vacancies are increased and the oxide semiconductor films 409 a,409 b, and 409 c have n-type conductivity in some cases. Thus, theconcentration of silicon or carbon in the oxide semiconductor films 409a, 409 b, and 409 c, particularly in the channel region, is set to belower than or equal to 2×10¹⁸ atoms/cm³, or lower than or equal to2×10¹⁷ atoms/cm³. As a result, the transistor has a positive thresholdvoltage (normally-off characteristics). Note that the concentration ofsilicon or carbon can be measured by secondary ion mass spectrometry(SIMS), for example.

Furthermore, the concentration of alkali metal or alkaline earth metalin the oxide semiconductor films 409 a, 409 b, and 409 c, which ismeasured by SIMS, can be lower than or equal to 1×10¹⁸ atoms/cm³ orlower than or equal to 2×10¹⁶ atoms/cm³. Alkali metal and alkaline earthmetal might generate carriers when bonded to an oxide semiconductor, inwhich case the off-state current of the transistor might be increased.Therefore, it is preferable to reduce the concentration of alkali metalor alkaline earth metal in the oxide semiconductor films 409 a, 409 b,and 409 c. As a result, the transistor has a positive threshold voltage(normally-off characteristics).

Furthermore, when nitrogen is contained in the oxide semiconductor films409 a, 409 b, and 409 c, electrons serving as carriers are generated andcarrier density is increased and the oxide semiconductor films 409 a,409 b, and 409 c have n-type conductivity in some cases. Thus, atransistor including an oxide semiconductor film which contains nitrogenis likely to have normally-on characteristics. For this reason, nitrogenin the oxide semiconductor films 409 a, 409 b, and 409 c is preferablyreduced as much as possible. For example, the nitrogen concentrationmeasured by SIMS may be 5×10¹⁸ atoms/cm³ or lower.

When impurity elements in the oxide semiconductor films 409 a, 409 b,and 409 c are reduced, the carrier density of the oxide semiconductorfilms can be lowered. Therefore, the oxide semiconductor films 409 a,409 b, and 409 c can have a carrier density less than or equal to 1×10¹⁷cm⁻³, less than or equal to 1×10¹⁵ cm⁻³, less than or equal to 1×10¹³cm³, or less than or equal to 1×10¹¹ cm⁻³.

When an oxide semiconductor film with a low impurity concentration and alow density of defect states is used as the oxide semiconductor films409 a, 409 b, and 409 c, the transistor can have more excellentelectrical characteristics. Here, the state in which the impurityconcentration is low and the density of defect states is low (the numberof oxygen vacancies is small) is referred to as “highly purifiedintrinsic”, “substantially highly purified intrinsic”, “intrinsic”, or“substantially intrinsic”. A highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor has few carrier generationsources and thus can have a low carrier density in some cases. Thus, atransistor whose channel region is formed in the oxide semiconductorfilm is likely to have a positive threshold voltage (normally-offcharacteristics). The highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has a low density of defectstates and accordingly has a low density of trap states in some cases.Furthermore, the highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film enables extremely lowoff-state current. Thus, the transistor whose channel region is formedin the oxide semiconductor film has little variation in electricalcharacteristics and high reliability in some cases.

Each of the oxide semiconductor films 409 a, 409 b, and 409 c may have anon-single-crystal structure. The non-single-crystal structure includesa c-axis aligned crystalline oxide semiconductor (CAAC-OS) describedlater, a polycrystalline structure, a microcrystalline structuredescribed later, or an amorphous structure, for example. Among thenon-single-crystal structures, the amorphous structure has the highestdensity of defect states, whereas the CAAC-OS has the lowest density ofdefect states.

Note that each of the oxide semiconductor films 409 a, 409 b, and 409 cmay be a single film or stacked films including two or more of thefollowing regions: a region having an amorphous structure, a regionhaving a microcrystalline structure, a region having a polycrystallinestructure, a CAAC-OS region, and a region having a single-crystalstructure.

[Liquid Crystal Layer]

As examples of the liquid crystal layer 620, thermotropic liquidcrystal, low-molecular liquid crystal, high-molecular liquid crystal,polymer dispersed liquid crystal, ferroelectric liquid crystal, andanti-ferroelectric liquid crystal are given. Alternatively, a liquidcrystal material which exhibits a cholesteric phase, a smectic phase, acubic phase, a chiral nematic phase, an isotropic phase, or the like maybe used. Furthermore, a liquid crystal material exhibiting a blue phasemay be used.

For a driving method of the liquid crystal layer 620, an in-planeswitching (IPS) mode, a twisted nematic (TN) mode, an FFS mode, anaxially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, or the likecan be used. In addition, the liquid crystal layer 620 can be driven by,for example, a vertical alignment (VA) mode such as a multi-domainvertical alignment (MVA) mode, a patterned vertical alignment (PVA)mode, an electrically controlled birefringence (ECB) mode, a continuouspinwheel alignment (CPA) mode, or an advanced super view (ASV) mode canbe used.

[EL Layer]

The EL layer 419 includes at least a light-emitting material. Examplesof the light-emitting material include an organic compound and aninorganic compound such as a quantum dot.

The organic compound and the inorganic compound can be formed by anevaporation method (including a vacuum evaporation method), an ink-jetmethod, a coating method, or gravure printing, for example.

Examples of materials that can be used for the organic compound includea fluorescent material and a phosphorescent material. A fluorescentmaterial is preferably used in terms of the lifetime, while aphosphorescent material is preferably used in terms of the efficiency.Furthermore, both of a fluorescent material and a phosphorescentmaterial may be used.

A quantum dot is a semiconductor nanocrystal with a size of severalnanometers and contains approximately 1×10³ to 1×10⁶ atoms. Since energyshift of quantum dots depend on their size, quantum dots made of thesame substance emit light with different wavelengths depending on theirsize; thus, emission wavelengths can be easily adjusted by changing thesize of quantum dots.

Since a quantum dot has an emission spectrum with a narrow peak,emission with high color purity can be obtained. In addition, a quantumdot is said to have a theoretical internal quantum efficiency ofapproximately 100%, which far exceeds that of a fluorescent organiccompound, i.e., 25%, and is comparable to that of a phosphorescentorganic compound. Therefore, a quantum dot can be used as alight-emitting material to obtain a light-emitting element having highlight-emitting efficiency. Furthermore, since a quantum dot which is aninorganic compound has high inherent stability, a light-emitting elementwhich is favorable also in terms of lifetime can be obtained.

Examples of a material of a quantum dot include a Group 14 element inthe periodic table, a Group 15 element in the periodic table, a Group 16element in the periodic table, a compound of a plurality of Group 14elements in the period table, a compound of an element belonging to anyof Groups 4 to 14 in the periodic table and a Group 16 element in theperiod table, a compound of a Group 2 element in the periodic table anda Group 16 element in the period table, a compound of a Group 13 elementin the period table and a Group 15 element in the period table, acompound of a Group 13 element in the period table and a Group 17element in the period table, a compound of a Group 14 element in theperiod table and a Group 15 element in the period table, a compound of aGroup 11 element in the period table and a Group 17 element in theperiod table, iron oxides, titanium oxides, spinel chalcogenides, andsemiconductor clusters.

Specific examples include, but are not limited to, cadmium selenide;cadmium sulfide; cadmium telluride; zinc selenide; zinc oxide; zincsulfide; zinc telluride; mercury sulfide; mercury selenide; mercurytelluride; indium arsenide; indium phosphide; gallium arsenide; galliumphosphide; indium nitride; gallium nitride; indium antimonide; galliumantimonide; aluminum phosphide; aluminum arsenide; aluminum antimonide;lead selenide; lead telluride; lead sulfide; indium selenide; indiumtelluride; indium sulfide; gallium selenide; arsenic sulfide; arsenicselenide; arsenic telluride; antimony sulfide; antimony selenide;antimony telluride; bismuth sulfide; bismuth selenide; bismuthtelluride; silicon; silicon carbide; germanium; tin; selenium;tellurium; boron; carbon; phosphorus; boron nitride; boron phosphide;boron arsenide; aluminum nitride; aluminum sulfide; barium sulfide;barium selenide; barium telluride; calcium sulfide; calcium selenide;calcium telluride; beryllium sulfide; beryllium selenide; berylliumtelluride; magnesium sulfide; magnesium selenide; germanium sulfide;germanium selenide; germanium telluride; tin sulfide; tin selenide; tintelluride; lead oxide; copper fluoride; copper chloride; copper bromide;copper iodide; copper oxide; copper selenide; nickel oxide; cobaltoxide; cobalt sulfide; triiron tetraoxide; iron sulfide; manganeseoxide; molybdenum sulfide; vanadium oxide; tungsten oxide; tantalumoxide; titanium oxide; zirconium oxide; silicon nitride; germaniumnitride; aluminum oxide; barium titanate; a compound of selenium, zinc,and cadmium; a compound of indium, arsenic, and phosphorus; a compoundof cadmium, selenium, and sulfur; a compound of cadmium, selenium, andtellurium; a compound of indium, gallium, and arsenic; a compound ofindium, gallium, and selenium; a compound of indium, selenium, andsulfur; a compound of copper, indium, and sulfur; and combinationsthereof. What is called an alloyed quantum dot, whose composition isrepresented by a given ratio, may be used. For example, an alloyedquantum dot of cadmium, selenium, and sulfur is a means effective inobtaining blue light because the emission wavelength can be changed bychanging the content ratio of elements.

As the quantum dot, any of a core-type quantum dot, a core-shell quantumdot, a core-multishell quantum dot, and the like can be used. Note thatwhen a core is covered with a shell formed of another inorganic materialhaving a wider band gap, the influence of defects and dangling bondsexisting at the surface of a nanocrystal can be reduced. Since such astructure can significantly improve the quantum efficiency of lightemission, it is preferable to use a core-shell or core-multishellquantum dot. Examples of the material of a shell include zinc sulfideand zinc oxide.

Quantum dots have a high proportion of surface atoms and thus have highreactivity and easily cohere together. For this reason, it is preferablethat a protective agent be attached to, or a protective group beprovided at the surfaces of quantum dots. The attachment of theprotective agent or the provision of the protective group can preventcohesion and increase solubility in a solvent. It can also reducereactivity and improve electrical stability. Examples of the protectiveagent (or the protective group) include polyoxyethylene alkyl etherssuch as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, andpolyoxyethylene oleyl ether; trialkylphosphines such astripropylphosphine, tributylphosphine, trihexylphosphine, andtrioctylphoshine; polyoxyethylene alkylphenyl ethers such aspolyoxyethylene n-octylphenyl ether and polyoxylethylene n-nonylphenylether; tertiary amines such as tri(n-hexyl)amine, tri(n-octyl)amine, andtri(n-decyl)amine; organophosphorus compounds such as tripropylphosphineoxide, tributylphosphine oxide, trihexylphosphine oxide,trioctylphosphine oxide, and tridecylphosphine oxide; polyethyleneglycol diesters such as polyethylene glycol dilaurate and polyethyleneglycol distearate; organic nitrogen compounds such asnitrogen-containing aromatic compounds, e.g., pyridines, lutidines,collidines, and quinolones; animoalkanes such as hexylamine, octylamine,decylamine, dodecylamine, tetradecylamine, hexadecylamine, andoctadecylamine; dialkylsulfides such as dibutylsulfide;dialkylsulfoxides such as dimethylsulfoxide and dibutylsulfoxide;organic sulfur compounds such as sulfur-containing aromatic compounds,e.g., thiophene; higher fatty acids such as a palmitin acid, a stearicacid, and an oleic acid; alcohols; sorbitan fatty acid esters; fattyacid modified polyesters; tertiary amine modified polyurethanes; andpolyethyleneimines.

Since band gaps of quantum dots are increased as their size isdecreased, the size is adjusted as appropriate so that light with adesired wavelength can be obtained. Light emission from the quantum dotsis shifted to a blue color side, i.e., a high energy side, as thecrystal size is decreased; thus, emission wavelengths of the quantumdots can be adjusted over a wavelength region of a spectrum of anultraviolet region, a visible light region, and an infrared region bychanging the size of quantum dots. The range of size (diameter) ofquantum dots which is usually used is 0.5 nm to 20 nm, preferably 1 nmto 10 nm. The emission spectra are narrowed as the size distribution ofthe quantum dots gets smaller, and thus light can be obtained with highcolor purity. The shape of the quantum dots is not particularly limitedand may be spherical shape, a rod shape, a circular shape, or the like.Quantum rods which are rod-like shape quantum dots emit directionallight polarized in the c-axis direction; thus, quantum rods can be usedas a light-emitting material to obtain a light-emitting element withhigher external quantum efficiency.

In most EL elements, to improve luminous efficiency, light-emittingmaterials are dispersed in host materials and the host materials need tobe substances each having a singlet excitation energy or a tripletexcitation energy higher than or equal to that of the light-emittingmaterial. In the case of using a blue phosphorescent material, it isparticularly difficult to develop a host material which has a tripletexcitation energy higher than or equal to that of the bluephosphorescent material and which is excellent in terms of a lifetime.On the other hand, even when a light-emitting layer is composed ofquantum dots and made without a host material, the quantum dots enableluminous efficiency to be ensured; thus, a light-emitting element whichis favorable in terms of a lifetime can be obtained. In the case wherethe light-emitting layer is composed of quantum dots, the quantum dotspreferably have core-shell structures (including core-multishellstructures).

[Alignment Film]

For the alignment films 618 a and 618 b, a material containing polyimideor the like can be used. For example, a material containing polyimide orthe like may be subjected to a rubbing process or an optical alignmentprocess to have alignment in a predetermined direction.

[Light-Blocking Film]

The light-blocking films 602 and 662 function as a black matrix. For thelight-blocking films 602 and 662, a material that prevents lighttransmission is used. Examples of the material that prevents lighttransmission include a metal material and an organic resin materialcontaining a black pigment.

[Color Film]

The color film 604 functions as a color filter. For the color film 604,a material transmitting light of a predetermined color (e.g., a materialtransmitting light of blue, green, red, yellow, or white) is used.

[Structure Body]

The structure bodies 610 a and 610 b have a function of providing acertain space between components between which the structure bodies 610a and 610 b are interposed. For each of the structure bodies 610 a and610 b, an organic material, an inorganic material, or a compositematerial of an organic material and an inorganic material can be used.For the inorganic material and the organic material, the materials forthe insulating films 404, 406, 408, 410 a, 410 b, 410 c, 412, 413, 416,418, and 606 can be used.

[Functional Film]

As the functional film 626, a polarizing plate, a retardation plate, adiffusing film, an anti-reflective film, a condensing film, or the likecan be used. As the functional film 626, an antistatic film preventingthe attachment of a foreign substance, a water repellent filmsuppressing the attachment of stain, a hard coat film suppressinggeneration of a scratch in use, or the like can be used.

[Sealing Material]

For the sealing material 454, an inorganic material, an organicmaterial, a composite material of an inorganic material and an organicmaterial, or the like can be used. Examples of the organic materialinclude a thermally fusible resin and a curable resin. As the sealingmaterial 454, an adhesive including a resin material (e.g., a reactivecurable adhesive, a photocurable adhesive, a thermosetting adhesive, oran anaerobic adhesive) may be used. Examples of such resin materialsinclude an epoxy resin, an acrylic resin, a silicone resin, a phenolresin, a polyimide resin, an imide resin, a polyvinyl chloride (PVC)resin, a polyvinyl butyral (PVB) resin, and an ethylene vinyl acetate(EVA) resin.

[Sealant]

For the sealant 622, the materials for the sealing material 454 can beused. For the sealant 622, a material such as glass frit may be used inaddition to the above materials. As a material used for the sealant 622,a material which is impermeable to moisture or oxygen is preferablyused.

[Electrode]

For the electrode 664, 665, and 667, the materials for the conductivefilm 402, 403 a, 403 b, 403 c, 405 a, 405 b, 405 c, 405 d, 407 a, 407 b,407 c, 407 d, 407 e, 411 a, 411 b, 411 c, 414 a, 414 b, 414 c, 414 d,414 e, 414 f, 414 g, 414 h, 417, 420, 608 described above can be used.Conductive nanowires may be used for the electrode 664, 665, and 667.The average diameter of the nanowire is greater than or equal to 1 nmand less than or equal to 100 nm, preferably greater than or equal to 5nm and less than or equal to 50 nm, more preferably greater than orequal to 5 nm and less than or equal to 25 nm. As the nanowire, a carbonnanotube or a metal nanowire such as an Ag nanowire, a Cu nanowire, andan Al nanowire can be used. For example, in the case where a Ag nanowireis used for any one of or all of the electrodes 664, 665, and 667, thetransmittance of visible light can be greater than or equal to 89% andthe sheet resistance can be greater than or equal to 40 Ω/square andless than or equal to 100 Ω/square.

As described above, the display device of one embodiment of the presentinvention includes two display elements. Furthermore, the display deviceincludes two transistors for driving the two display elements. Onedisplay element functions as a reflective liquid crystal element and theother display element functions as a transmissive EL element; thus, anovel display device that is highly convenient or reliable can beprovided. With the transmissive EL elements in adjacent pixels arrangedin different positions, the manufacturing yield in the case where the ELelements are separately formed can be increased and a display devicewith high productivity can be provided.

The structure described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 2

In this embodiment, a display element having a function of emittinglight is described in detail.

<2-1. Structure Example 1 of Display Element>

FIG. 26 is a cross-sectional view illustrating details of the displayelement 12 described in Embodiment 1.

The display element 12 illustrated in FIG. 26 includes a light-emittingelement 12R, a light-emitting element 12G, and a light-emitting element12B.

The light-emitting element 12R includes a conductive film 417R, the ELlayer 419 over the conductive film 417R, and the conductive film 420over the EL layer 419. The light-emitting element 12G includes aconductive film 417G, the EL layer 419 over the conductive film 417G,and the conductive film 420 over the EL layer 419. The light-emittingelement 12B includes a conductive film 417B, the EL layer 419 over theconductive film 417B, and the conductive film 420 over the EL layer 419.The conductive films for the light-emitting elements (the conductivefilms 417R, 417G, and 417B) are separated by the insulating films 418.

The light-emitting element 12R includes the conductive film 417R overthe substrate 401, a hole-injection layer 419 _(HIL) over the conductivefilm 417R, the hole-transport layer 419 _(HTL) over the hole-injectionlayer 419 _(HIL), a light-emitting layer 419 _(EML(R)) over thehole-transport layer 419 _(HTL), a light-emitting layer 419 _(EML(B))over the light-emitting layer 419 _(EML(R)), an electron-transport layer419 _(ETL) over the light-emitting layer 419 _(EML(B)), and anelectron-injection layer 419 _(EIL) over the electron-transport layer419 _(ETL).

The light-emitting element 12G includes the conductive film 417G overthe substrate 401, the hole-injection layer 419 _(HIL) over theconductive film 417G, the hole-transport layer 419 _(HTL) over thehole-injection layer 419 _(HIL), a light-emitting layer 419 _(EML(G))over the hole-transport layer 419 _(HTL), the light-emitting layer 419_(EML(B)) over the light-emitting layer 419 _(EML(G)), theelectron-transport layer 419 _(ETL) over the light-emitting layer 419_(EML(B)), and the electron-injection layer 419 _(EIL) over theelectron-transport layer 419 _(ETL).

The light-emitting element 12B includes the conductive film 417B overthe substrate 401, the hole-injection layer 419 _(HIL) over theconductive film 417B, the hole-transport layer 419 _(HTL) over thehole-injection layer 419 _(HIL), the light-emitting layer 419 _(EML(B))over the hole-transport layer 419 _(HTL), the electron-transport layer419 _(ETL) over the light-emitting layer 419 _(EML(B)), and theelectron-injection layer 419 _(EIL) over the electron-transport layer419 _(ETL).

In the display element 12 illustrated in FIG. 26, the hole-injectionlayer 419 _(HIL), the hole-transport layer 419 _(HTL), thelight-emitting layer 419 _(EML(B)), the electron-transport layer 419_(ETL), and the electron-injection layer 419 _(EIL) are used in commonby the light-emitting element 12R, the light-emitting element 12G, andthe light-emitting element 12B.

With such a structure, the manufacturing yield of the display element 12can be increased. Specifically, a separate formation process (i.e., aseparate coloring process) of the light-emitting elements in the displayelement 12 can be two steps, coloring for the light-emitting layer 419_(EML(R)) and coloring for the light-emitting layer 419 _(EML(G)).

Note that the light-emitting layer 419 _(EML(B)) does not contribute tolight emission in the light-emitting element 12R and the light-emittingelement 12G. For example, for the light-emitting layer 419 _(EML(B)), amaterial with a high electron-transport property and a lowhole-transport property or a material whose highest occupied molecularorbital (HOMO) level is lower than the HOMO level of materials used forthe light-emitting layer 419 _(EML(R)) and the light-emitting layer 419_(EML(G)) is used. That is, in the light-emitting element 12R and thelight-emitting element 12G, the light-emitting layer 419 _(EML(B))functions as an electron-transport layer.

For example, in the case where the light-emitting layer 419 _(EML(B))includes a host material and a guest material (a light-emittingmaterial), it is preferable that the host material have anelectron-transport property and that the guest material have a hole-trapproperty. With such a structure, carriers can be efficiently recombinedin the light-emitting layer 419 _(EML(R)) and the light-emitting layer419 _(EML(G)).

In the case where each of the light-emitting layer 419 _(EML(R)) and thelight-emitting layer 419 _(EML(G)) includes a host material and a guestmaterial (a light-emitting material), it is preferable that the hostmaterial have a hole-transport property and an electron-transportproperty. With such a structure, each of the light-emitting layer 419_(EML(R)) and the light-emitting layer 419 _(EML(G)) has a bipolarproperty.

Each of the light-emitting layer 419 _(EML(R)) and the light-emittinglayer 419 _(EML(G)) includes a phosphorescent material as a guestmaterial. The light-emitting layer 419 _(EML(B)) includes a fluorescentmaterial as a guest material. With such a structure, a display elementwith high emission efficiency and high reliability can be provided. Forexample, a phosphorescent material emitting light in a red wavelengthrange can be used in the light-emitting layer 419 _(EML(R)), aphosphorescent material emitting light in a green wavelength range canbe used in the light-emitting layer 419 _(EML(G)), and a fluorescentmaterial emitting light in a blue wavelength range can be used in thelight-emitting layer 419 _(EML(B)). Note that materials that can be usedin the light-emitting layer 419 _(EML(R)), the light-emitting layer 419_(EML(G)), and the light-emitting layer 419 _(EML(B)) are not limited tothe above. For example, a phosphorescent material may be used in thelight-emitting layer 419 _(EML(B)).

With the above-described structure, the number of steps of the separatecoloring process in manufacturing the light-emitting elements is small;thus, a display element with high productivity can be provided. Thelight-emitting elements of the display element have low powerconsumption because of their high emission efficiency. Moreover, thelight-emitting elements have high reliability. Therefore, a noveldisplay element with high productivity and low power consumption can beprovided.

Next, components in the display element 12 illustrated in FIG. 26 aredescribed below.

[Conductive Film]

For the conductive films 417R, 417G, 417B, and 420, the materials forthe conductive films 402, 403 a, 403 b, 403 c, 405 a, 405 b, 405 c, 405d, 407 a, 407 b, 407 c, 407 d, 407 e, 411 a, 411 b, 411 c, 414 a, 414 b,414 c, 414 d, 414 e, 414 f, 414 g, 414 h, 417, 420, 608, and 682described in Embodiment 1 can be used. In particular, ITO or ITSO ispreferably used for the conductive film 417R, the conductive film 417G,and the conductive film 417B. A metal film with high reflectancecontaining Al or Ag is preferably used for the conductive film 420.

[Insulating Film]

For the insulating film 418, the materials for the insulating films 404,406, 408, 410 a, 410 b, 410 c, 412, 413, 416, 418, 606, 663, 666, 668,and 681 described in Embodiment 1 can be used.

[Light-Emitting Layer]

Light emitted from the light-emitting layer 419 _(EML(R)) has a peak ina red wavelength range. Light emitted from the light-emitting layer 419_(EML(G)) has a peak in a green wavelength range. Light emitted from thelight-emitting layer 419 _(EML(B)) has a peak in a blue wavelengthrange. For example, it is preferable that phosphorescent materials beused for the light-emitting layer 419 _(EML(R)) and the light-emittinglayer 419 _(EML(G)), and a fluorescent material be used for thelight-emitting layer 419 _(EML(B)). Each of the light-emitting layer 419_(EML(R)) and the light-emitting layer 419 _(EML(G)) includes either anelectron-transport material or a hole-transport material or both, inaddition to the phosphorescent material. The light-emitting layer 419_(EML(B)) includes either an electron-transport material or ahole-transport material or both, in addition to the fluorescentmaterial.

[Phosphorescent Material]

As the phosphorescent material, an iridium-, rhodium-, or platinum-basedorganometallic complex or metal complex can be used; in particular, anorganoiridium complex such as an iridium-based ortho-metalated complexis preferable. As an ortho-metalated ligand, a 4H-triazole ligand, a1H-triazole ligand, an imidazole ligand, a pyridine ligand, a pyrimidineligand, a pyrazine ligand, an isoquinoline ligand, or the like can beused. As the metal complex, a platinum complex having a porphyrin ligandor the like can be used.

Examples of the substance that has an emission peak in the blue or greenwavelength range include organometallic iridium complexes having a4H-triazole skeleton, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III)(abbreviation: Ir(mpptz-dmp)₃),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Mptz)₃),tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPrptz-3b)₃), andtris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPr5btz)₃); organometallic iridium complexes having a1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(Mptz1-mp)₃) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Prptz1-Me)₃); organometallic iridium complexes havingan imidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: Ir(iPrpmi)₃) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: Ir(dmpimpt-Me)₃); and organometallic iridium complexes inwhich a phenylpyridine derivative having an electron-withdrawing groupis a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)).

Examples of the substance that has an emission peak in the green oryellow wavelength range include organometallic iridium complexes havinga pyrimidine skeleton, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:Ir(mppm)₃), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₃),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(abbreviation: Ir(nbppm)₂(acac)),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(mpmppm)₂(acac)),(acetylacetonato)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III)(abbreviation: Ir(dmppm-dmp)₂(acac)),(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: Ir(dppm)₂(acac)); organometallic iridium complexes havinga pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)); organometallic iridium complexeshaving a pyridine skeleton, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(ppy)₂(acac)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)₃),tris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),and bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(pq)₂(acac)); organometallic iridium complexes such asbis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)), andbis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)); and a rare earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)). Among the materials given above, the organometalliciridium complexes having a pyrimidine skeleton have distinctively highreliability and emission efficiency and are thus particularlypreferable.

Examples of the substance that has an emission peak in the yellow or redwavelength range include organometallic iridium complexes having apyrimidine skeleton, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: Ir(5mdppm)₂(dibm)),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(5mdppm)₂(dpm)), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(dlnpm)₂(dpm)); organometallic iridium complexes havinga pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm)), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)); organometallic iridium complexes havinga pyridine skeleton, such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:Ir(piq)₃) andbis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)); a platinum complex such as2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). Among the materials given above, theorganometallic iridium complexes having a pyrimidine skeleton havedistinctively high reliability and emission efficiency and are thusparticularly preferable. Further, the organometallic iridium complexeshaving a pyrazine skeleton can provide red light emission with favorablechromaticity.

As the material included in the light-emitting layer, any material canbe used as long as the material can convert the triplet excitationenergy into light emission. As an example of the material that canconvert triplet excitation energy into light emission, a thermallyactivated delayed fluorescence material is given in addition to thephosphorescent material. Therefore, the term “phosphorescent material”in the description can be replaced with the term “thermally activateddelayed fluorescence material”. The thermally activated delayedfluorescence material is a material having a small energy differencebetween the singlet excitation energy level and the triplet excitationenergy level and has a function of converting the triplet excitationenergy into the singlet excitation energy by reverse intersystemcrossing. Thus, the thermally activated delayed fluorescence materialcan up-convert a triplet excited state into a singlet excited state(i.e., reverse intersystem crossing is possible) using a little thermalenergy and efficiently exhibit light emission (fluorescence) from thesinglet excited state. Conditions for efficiently obtaining thermallyactivated delayed fluorescence are as follows: the energy differencebetween the singlet excitation energy level and the triplet excitationenergy level is preferably greater than 0 eV and less than or equal to0.2 eV, more preferably greater than 0 eV and less than or equal to 0.1eV.

As examples of the thermally activated delayed fluorescence material, afullerene, a derivative thereof, an acridine derivative such asproflavine, and eosin are given. Furthermore, a metal-containingporphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn),cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd),is given.

As the thermally activated delayed fluorescence material composed of onekind of material, a heterocyclic compound including a π-electron richheteroaromatic ring and a π-electron deficient heteroaromatic ring canalso be used. Specifically,2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(abbreviation: PIC-TRZ),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn),2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine(abbreviation: PXZ-TRZ),3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole(abbreviation: PPZ-3TPT),3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation:ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone(abbreviation: DMAC-DPS), or10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation:ACRSA) can be used. The heterocyclic compound is preferably used becauseof having the π-electron rich heteroaromatic ring and the π-electrondeficient heteroaromatic ring, for which the electron-transport propertyand the hole-transport property are high. Note that a substance in whichthe π-electron rich heteroaromatic ring is directly bonded to theπ-electron deficient heteroaromatic ring is particularly preferably usedbecause the donor property of the π-electron rich heteroaromatic ringand the acceptor property of the π-electron deficient heteroaromaticring are both increased and the difference between the level of thesinglet excited state and the level of the triplet excited state becomessmall.

[Fluorescent Material]

The fluorescent material is preferably, but not particularly limited to,an anthracene derivative, a tetracene derivative, a chrysene derivative,a phenanthrene derivative, a pyrene derivative, a perylene derivative, astilbene derivative, an acridone derivative, a coumarin derivative, aphenoxazine derivative, a phenothiazine derivative, or the like, and forexample, any of the following materials can be used.

The examples include5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-bis(4-tert-butylphenyl)pyrene-1,6-diamine(abbreviation: 1,6tBu-FLPAPrn),N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-3,8-dicyclohexylpyrene-1,6-diamine(abbreviation: ch-1,6FLPAPrn),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBCl), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 6, coumarin 545T,N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene,2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene(abbreviation: TBRb), Nile red,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation:DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB), 2-(2,6-bis {2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM),2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM), and5,10,15,20-tetraphenylbisbenzo[5,6]indeno[1,2,3-cd:1′,2′,3′-lm]perylene.

[Host Material]

In the light-emitting layer, the light-emitting material is preferablydispersed in the host material. In this case, the weight ratio of thehost material to the light-emitting material is larger. A variety ofmaterials can be used as the host material. For example, a materialhaving a function of transporting a hole (a hole-transport material) anda material having a function of transporting an electron (anelectron-transport material) can be used. Furthermore, a bipolarmaterial having a hole-transport property and an electron-transportproperty can be used.

As the host material, a material having a property of transporting moreelectrons than holes can be used, and a material having an electronmobility of 1×10⁻⁶ cm²/Vs or higher is preferable. A compound includinga π-electron deficient heteroaromatic ring skeleton such as anitrogen-containing heteroaromatic compound, or a zinc- oraluminum-based metal complex can be used, for example, as the materialwhich easily accepts electrons (the material having anelectron-transport property). Specific examples include a metal complexhaving a quinoline ligand, a benzoquinoline ligand, an oxazole ligand,and a thiazole ligand. In addition, a compound such as an oxadiazolederivative, a triazole derivative, a benzimidazole derivative, aquinoxaline derivative, a dibenzoquinoxaline derivative, aphenanthroline derivative, a pyridine derivative, a bipyridinederivative, a pyrimidine derivative, and a triazine derivative can begiven.

Specific examples include metal complexes having a quinoline orbenzoquinoline skeleton, such as tris(8-quinolinolato)aluminum(III)(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III)(abbreviation: Almq₃), bis(10-hydroxybenzo[h] quinolinato)beryllium(II)(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), and bis(8-quinolinolato)zinc(II) (abbreviation:Znq). Alternatively, a metal complex having an oxazole-based orthiazole-based ligand, such as bis[2-(2-benzoxazolyl)phenolate]zinc(II)(abbreviation: ZnPBO) or bis[2-(2-benzothiazolyl)phenolato]zinc(II)(abbreviation: ZnBTZ) can be used. Other than such metal complexes, anyof the following can be used: heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),9-[4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl]-9H-carbazole(abbreviation: CzTAZ1),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), bathophenanthroline (abbreviation: BPhen),and bathocuproine (abbreviation: BCP); heterocyclic compounds having adiazine skeleton such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDB q-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II),2-[3-(3,9′-bi-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzCzPDBq),4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine(abbreviation: 4,6mDBTP2Pm-II), and4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation:4,6mCzP2Pm); heterocyclic compounds having a triazine skeleton such as2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn); heterocyclic compounds having a pyridineskeleton such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine(abbreviation: 35DCzPPy); and heteroaromatic compounds such as4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs). Amongthe heterocyclic compounds, the heterocyclic compounds having a triazineskeleton, a diazine (pyrimidine, pyrazine, pyridazine) skeleton, or apyridine skeleton are highly reliable and stable and are thus preferablyused. In addition, the heterocyclic compounds having the skeletons havea high electron-transport property to contribute to a reduction indriving voltage. Further alternatively, a high molecular compound suchas poly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used. The substances described here aremainly substances having an electron mobility of 1×10⁻⁶ cm²/Vs orhigher. Note that other substances may also be used as long as theirelectron-transport properties are higher than their hole-transportproperties.

As the host material, hole-transport materials given below can be used.

A material having a property of transporting more holes than electronscan be used as the hole-transport material, and a material having a holemobility of 1×10⁻⁶ cm²Ns or higher is preferable. Specifically, anaromatic amine, a carbazole derivative, an aromatic hydrocarbon, astilbene derivative, or the like can be used. Furthermore, thehole-transport material may be a high molecular compound.

Specific examples of the material having a high hole-transport propertyinclude N,N′-di(p-tolyl)-N,N-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD), and1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B).

Specific examples of the carbazole derivative are3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Other examples of the carbazole derivative include4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA), and1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

Examples of the aromatic hydrocarbon are2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, and 2,5,8,11-tetra(tert-butyl)perylene.Other examples are pentacene and coronene. The aromatic hydrocarbonhaving a hole mobility of 1×10⁻⁶ cm²/Vs or higher and having 14 to 42carbon atoms is particularly preferable.

The aromatic hydrocarbon may have a vinyl skeleton. Examples of thearomatic hydrocarbon having a vinyl group are4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi),9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA),and the like.

Other examples are high molecular compounds such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD).

Examples of the material having a high hole-transport property arearomatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB ora-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N-phenyl-N-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),4-phenyldiphenyl-(9-phenyl-9H-carbazol-3-yl)amine (abbreviation:PCA1BP), N,N′-bis(9-phenylcarbazol-3-yl)-N,N-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N,N′,N″-triphenyl-N,N′,N→-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine(abbreviation: PCBiF),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF),N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N-[4-(9H-carbazol-9-yl)phenyl]-N-(4-phenyl)phenylaniline (abbreviation:YGA1BP), andN,N′-bis[4-(carbazol-9-yl)phenyl]-N,N-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F). Other examples are amine compounds, carbazolecompounds, thiophene compounds, furan compounds, fluorene compounds;triphenylene compounds; phenanthrene compounds, and the like such as3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPN),3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPPn), 3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP),1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP),3,6-di(9H-carbazol-9-yl)-9-phenyl-9H-carbazole (abbreviation: PhCzGI),2,8-di(9H-carbazol-9-yl)-dibenzothiophene (abbreviation: Cz2DBT),4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II),4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II),1,3,5-tri(dibenzothiophen-4-yl)-benzene (abbreviated as DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III),4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV), and4-[3-(triphenylene-2-yl)phenyl]dibenzothiophene (abbreviation:mDBTPTp-II). Among the above compounds, compounds including a pyrroleskeleton, a furan skeleton, a thiophene skeleton, or an aromatic amineskeleton are preferred because of their high stability and reliability.In addition, the compounds having such skeletons have a highhole-transport property to contribute to a reduction in driving voltage.

It is preferable that the host material and the phosphorescent materialbe selected such that the emission peak of the host material overlapswith an absorption band, specifically an absorption band on the longestwavelength side, of a triplet metal to ligand charge transfer (MLCT)transition of the phosphorescent material. This makes it possible toprovide a light-emitting element with drastically improved emissionefficiency. Note that in the case where a thermally activated delayedfluorescent material is used instead of the phosphorescent material, itis preferable that the absorption band on the longest wavelength side bea singlet absorption band.

Note that the host material may be a mixture of a plurality of kinds ofsubstances, and in the case of using a mixed host material, it ispreferable to mix a material having an electron-transport property witha material having a hole-transport property. By mixing the materialhaving an electron-transport property with the material having ahole-transport property, the carrier transport property of thelight-emitting layer can be easily adjusted and a recombination regioncan be easily controlled. The content ratio (weight ratio) of thematerial having an electron-transport property to the material having ahole-transport property is preferably 1:9 to 9:1.

An exciplex may be formed by these mixed materials. It is preferablethat the combination of the materials be selected so as to form anexciplex that exhibits light emission whose wavelength overlaps with awavelength of a lowest-energy-side absorption band of the light-emittingmaterial, in which case excitation energy is transferred smoothly fromthe exciplex to the light-emitting material, light emission can beobtained efficiently from the light-emitting material, and the drivingvoltage can be reduced.

In the light-emitting layer, a material other than the host material andthe light-emitting material may be contained. Besides theabove-mentioned materials, an inorganic compound or a high molecularcompound (e.g., an oligomer, a dendrimer, and a polymer) may be used.

In the case of using quantum dots as the light-emitting material in thelight-emitting layer, the thickness of the light-emitting layer is setto 3 nm to 100 nm, preferably 10 nm to 100 nm, and the light-emittinglayer is made to contain 1 volume % to 100 volume % of the quantum dots.Note that it is preferable that the light-emitting layer be composed ofthe quantum dots. To form a light-emitting layer in which the quantumdots are dispersed as light-emitting materials in host materials, thequantum dots may be dispersed in the host materials, or the hostmaterials and the quantum dots may be dissolved or dispersed in anappropriate liquid medium, and then a wet process (e.g., a spin coatingmethod, a casting method, a die coating method, blade coating method, aroll coating method, an ink-jet method, a printing method, a spraycoating method, a curtain coating method, or a Langmuir-Blodgett method)may be employed. For a light-emitting layer containing a phosphorescentsubstance, a vacuum evaporation method, as well as the wet process, canbe suitably employed.

An example of the liquid medium used for the wet process is an organicsolvent of ketones such as methyl ethyl ketone and cyclohexanone; fattyacid esters such as ethyl acetate; halogenated hydrocarbons such asdichlorobenzene; aromatic hydrocarbons such as toluene, xylene,mesitylene, and cyclohexylbenzene; aliphatic hydrocarbons such ascyclohexane, decalin, and dodecane; dimethylformamide (DMF); dimethylsulfoxide (DMSO); or the like.

[Hole-Injection Layer and Hole-Transport Layer]

The hole-injection layer 419 _(HIL) injects holes to the light-emittinglayer 419 _(EML(R)), the light-emitting layer 419 _(EML(G)), and thelight-emitting layer 419 _(EML(B)) through the hole-transport layer 419_(HTL) having a high hole-transport property, and contains ahole-transport material and an acceptor substance. When a hole-transportmaterial and an acceptor substance are contained, electrons areextracted from the hole-transport material by the acceptor substance togenerate holes, and the holes are injected into the light-emitting layer419 _(EML(R)), the light-emitting layer 419 _(EML(G)), and thelight-emitting layer 419 _(EML(B)) through the hole-transport layer 419_(HTL). Note that the hole-transport layer 419 _(HTL) is formed with ahole-transport material.

As the hole-transport materials used for the hole-injection layer 419_(HIL) and the hole-transport layer 419 _(HTL), the above-describedhole-transport materials that can be used for the light-emitting layer419 _(EML(R)), the light-emitting layer 419 _(EML(G)), and thelight-emitting layer 419 _(EML(B)) can be used.

Examples of the acceptor substance that is used for the hole-injectionlayer 419 _(HIL) include oxides of metals belonging to Groups 4 to 8 ofthe periodic table. Specifically, molybdenum oxide is particularlypreferable.

The hole-injection layers 419 _(HIL) in the light-emitting elements maybe formed with different materials and may have different thicknessesdepending on circumstances. The hole-transport layers 419 _(HTL) in thelight-emitting elements may be formed with different materials and mayhave different thicknesses depending on circumstances.

[Electron-Transport Layer]

For the electron-transport layer 419 _(ETL), the above-describedelectron-transport materials for the light-emitting layer 419 _(EML(R)),the light-emitting layer 419 _(EML(G)), and the light-emitting layer 419_(EML(B)) can be used.

[Electron-Injection Layer]

The electron-injection layer 419 _(EIL) is a layer containing asubstance with a high electron-injection property. For theelectron-injection layer 419 _(EIL), an alkali metal, an alkaline earthmetal, or a compound thereof, such as lithium fluoride (LiF), cesiumfluoride (CsF), calcium fluoride (CaF₂), or lithium oxide (LiO_(x)), canbe used. Alternatively, a rare earth metal compound such as erbiumfluoride (ErF₃) can be used. Electride may also be used for theelectron-injection layer 419 _(EIL). Examples of the electride include asubstance in which electrons are added at high concentration to calciumoxide-aluminum oxide.

Alternatively, the electron-injection layer 419 _(EIL) may be formedusing a composite material in which an organic compound and an electrondonor (donor) are mixed. The composite material is superior in anelectron-injection property and an electron-transport property, sinceelectrons are generated in the organic compound by the electron donor.The organic compound here is preferably a material excellent intransporting the generated electrons; specifically, for example, thesubstances for forming the electron-transport layer 419 _(ETL) (e.g., ametal complex or a heteroaromatic compound) can be used. As the electrondonor, a substance showing an electron-donating property with respect tothe organic compound may be used. Specifically, an alkali metal, analkaline earth metal, and a rare earth metal are preferable, andlithium, cesium, magnesium, calcium, erbium, ytterbium, and the like aregiven. Furthermore, an alkali metal oxide or an alkaline earth metaloxide is preferable, and for example, lithium oxide, calcium oxide,barium oxide, and the like can be given. Alternatively, Lewis base suchas magnesium oxide can also be used. An organic compound such astetrathiafulvalene (abbreviation: TTF) can also be used.

The electron-injection layers 419 _(EIL) in the light-emitting elementsmay be formed with different materials and may have differentthicknesses depending on circumstances. The electron-transport layers419 _(ETL) in the light-emitting elements may be formed with differentmaterials and may have different thicknesses depending on circumstances.

<2-2. Method for Manufacturing Display Element>

Next, a method for manufacturing the display element 12 of oneembodiment of the present invention is described below with reference toFIGS. 27A to 27C and FIGS. 28A and 28B.

FIGS. 27A to 27C and FIGS. 28A and 28B are cross-sectional viewsillustrating the method for manufacturing the display element 12 of oneembodiment of the present invention. The method for manufacturing thedisplay element 12 described below includes first to fifth steps.

[First Step]

In a first step, the conductive films (the conductive film 417R, theconductive film 417G, and the conductive film 417B) which function aslower electrodes of the light-emitting elements and the insulating films418 that cover end portions of the conductive films of thelight-emitting elements are formed (see FIG. 27A).

In the first step, there is no possibility of damaging a light-emittinglayer containing an organic compound, and thus a variety ofmicromachining technologies can be employed. In this embodiment, alight-transmitting conductive film is formed over the substrate 401 by asputtering method, the conductive film is patterned, and then theconductive film is processed into island shapes, whereby the conductivefilm 417R, the conductive film 417G, and the conductive film 417B areformed.

Next, the insulating films 418 are formed to cover the end portions ofthe conductive film 417R, the conductive film 417G, and the conductivefilm 417B. Note that the insulating films 418 have openings that overlapwith the conductive films (the conductive film 417R, the conductive film417G, and the conductive film 417B). The conductive films exposed in theopenings function as the lower electrodes of the light-emittingelements.

In this embodiment, in the first step, ITO is used for the conductivefilms 417R, 417G, and 417B, and an acrylic resin is used for theinsulating film 418.

Note that transistors or the like may be formed over the substrate 401before the first step. The transistors may be electrically connected tothe conductive films (the conductive film 417R, the conductive film417G, and the conductive film 417B).

[Second Step]

In the second step, the hole-injection layer 419 _(HIL) and thehole-transport layer 419 _(HTL) are formed over the conductive films(the conductive film 417R, the conductive film 417G, and the conductivefilm 417B) and the insulating films 418 (see FIG. 27B).

In the second step, the hole-injection layer 419 _(HIL) and thehole-transport layer 419 _(HTL) are formed by evaporation of an organiccompound. Note that the hole-injection layer 419 _(HIL) and thehole-transport layer 419 _(HTL) can be used in common by thelight-emitting elements, leading to a reduced manufacturing cost andimproved productivity.

[Third Step]

In the third step, the light-emitting layer 419 _(EML(R)) is formedusing a shadow mask 481 (see FIG. 27C).

Note that the shadow mask 481 is a shielding plate provided with anopening 482 and formed of foil of a metal or the like with a thicknessgreater than or equal to several tens of micrometers or a plate of ametal or the like with a thickness greater than or equal to severalhundreds of micrometers.

In the third step, the substrate 401 is introduced into an evaporationapparatus, and the shadow mask 481 is provided on the evaporation source(not illustrated) side. Next, alignment for providing the opening 482 ofthe shadow mask 481 in a desired position is performed. Here, theopening 482 is disposed to overlap with the conductive film 417R, and anorganic compound is deposited above the shadow mask 481, whereby thelight-emitting layer 419 _(EML(R)) is formed.

[Fourth Step]

In the fourth step, the light-emitting layer 419 _(EML(G)) is formedover the hole-transport layer 419 _(HTL) (see FIG. 28A).

In the fourth step, the substrate 401 is introduced into an evaporationapparatus, and the shadow mask 481 is provided on the evaporation source(not illustrated) side. Next, alignment for providing the opening 482 ofthe shadow mask 481 in a desired position is performed. Here, theopening 482 is disposed to overlap with the conductive film 417G, and anorganic compound is deposited above the shadow mask 481, whereby thelight-emitting layer 419 _(EML(G)) is formed.

In one embodiment of the present invention, as described in Embodiment1, a space between adjacent pixels is wide, and thus the margin forseparate coloring is wide. Therefore, a display element with a highmanufacturing yield can be provided.

[Fifth Step]

In the fifth step, the light-emitting layer 419 _(EML(B)), theelectron-transport layer 419 _(ETL), the electron-injection layer 419_(EIL), and the conductive film 420 are formed over the hole-transportlayer 419 _(HTL), the light-emitting layer 419 _(EML(R)), and thelight-emitting layer 419 _(EML(G)) (see FIG. 28B).

Note that the light-emitting layer 419 _(EML(B)), the electron-transportlayer 419 _(ETL), the electron-injection layer 419 _(EIL), and theconductive film 420 can be used in common by the light-emittingelements, leading to a reduced manufacturing cost and improvedproductivity.

Through the above steps, the display element 12 illustrated in FIG. 26can be manufactured. Note that in this embodiment, a separate coloringprocess of the light-emitting elements can be two steps, coloring forthe light-emitting layer 419 _(EML(R)) and coloring for thelight-emitting layer 419 _(EML(G)). As a result, a method formanufacturing a display element with high productivity can be provided.Consequently, a method for manufacturing a novel display element inwhich a decrease in aperture ratio accompanied by fabrication of ahigh-definition element is suppressed can be provided. Alternatively, anovel display element that can be produced easily can be provided.

This embodiment can be combined as appropriate with any of the otherembodiments.

Embodiment 3

In this embodiment, a transistor that can be used for the display deviceof one embodiment of the present invention is described in detail.

In this embodiment, a transistor with a staggered (top-gate) structureis described with reference to FIGS. 29A to 29C, FIGS. 30A to 30C, FIGS.31A and 31B, FIGS. 32A and 32B, FIGS. 33A and 33B, FIGS. 34A and 34B,FIGS. 35A and 35B, and FIGS. 36A to 36C.

<3-1. Structure Example 1 of Transistor>

FIG. 29A is a top view of a transistor 100. FIG. 29B is across-sectional view taken along a dashed-dotted line X1-X2 in FIG. 29A.FIG. 29C is a cross-sectional view taken along a dashed-dotted lineY1-Y2 in FIG. 29A. For clarity, FIG. 29A does not illustrate somecomponents such as an insulating film 110. As in FIG. 29A, somecomponents are not illustrated in some cases in top views of transistorsdescribed below. Furthermore, the direction of the dashed-dotted lineX1-X2 may be referred to as a channel length (L) direction, and thedirection of the dashed-dotted line Y1-Y2 may be referred to as achannel width (W) direction.

The transistor 100 illustrated in FIGS. 29A to 29C includes aninsulating film 104 over a substrate 102; an oxide semiconductor film108 over the insulating film 104; the insulating film 110 over the oxidesemiconductor film 108; a conductive film 112 over the insulating film110; and an insulating film 116 over the insulating film 104, the oxidesemiconductor film 108, and the conductive film 112. Note that the oxidesemiconductor film 108 includes a channel region 108 i overlapping withthe conductive film 112, a source region 108 s in contact with theinsulating film 116, and a drain region 108 d in contact with theinsulating film 116.

Furthermore, the insulating film 116 contains nitrogen or hydrogen. Theinsulating film 116 is in contact with the source region 108 s and thedrain region 108 d, so that nitrogen or hydrogen that is contained inthe insulating film 116 is added to the source region 108 s and thedrain region 108 d. The source region 108 s and the drain region 108 deach have a high carrier density when nitrogen or hydrogen is addedthereto.

The transistor 100 may further include an insulating film 118 over theinsulating film 116, a conductive film 120 a electrically connected tothe source region 108 s through an opening 141 a provided in theinsulating films 116 and 118, and a conductive film 120 b electricallyconnected to the drain region 108 d through an opening 141 b provided inthe insulating films 116 and 118.

In this specification and the like, the insulating film 104 may bereferred to as a first insulating film, the insulating film 110 may bereferred to as a second insulating film, the insulating film 116 may bereferred to as a third insulating film, and the insulating film 118 maybe referred to as a fourth insulating film. The conductive film 112functions as a gate electrode, the conductive film 120 a functions as asource electrode, and the conductive film 120 b functions as a drainelectrode.

The insulating film 110 functions as a gate insulating film. Theinsulating film 110 includes an excess oxygen region. Since theinsulating film 110 includes the excess oxygen region, excess oxygen canbe supplied to the channel region 108 i included in the oxidesemiconductor film 108. As a result, oxygen vacancies that might beformed in the channel region 108 i can be filled with excess oxygen,which can provide a highly reliable semiconductor device.

To supply excess oxygen to the oxide semiconductor film 108, excessoxygen may be supplied to the insulating film 104 that is formed underthe oxide semiconductor film 108. However, in that case, excess oxygencontained in the insulating film 104 might also be supplied to thesource region 108 s and the drain region 108 d included in the oxidesemiconductor film 108. When excess oxygen is supplied to the sourceregion 108 s and the drain region 108 d, the resistance of the sourceregion 108 s and the drain region 108 d might be increased.

In contrast, in the structure in which the insulating film 110 formedover the oxide semiconductor film 108 contains excess oxygen, excessoxygen can be selectively supplied only to the channel region 108 i.Alternatively, the carrier density of the source and drain regions 108 sand 108 d can be selectively increased after excess oxygen is suppliedto the channel region 108 i and the source and drain regions 108 s and108 d, in which case an increase in the resistance of the source anddrain regions 108 s and 108 d can be prevented.

Furthermore, each of the source region 108 s and the drain region 108 dincluded in the oxide semiconductor film 108 preferably contains anelement that forms an oxygen vacancy or an element that is bonded to anoxygen vacancy. Typical examples of the element that forms an oxygenvacancy or the element that is bonded to an oxygen vacancy includehydrogen, boron, carbon, nitrogen, fluorine, phosphorus, sulfur,chlorine, titanium, and a rare gas. Typical examples of the rare gaselement are helium, neon, argon, krypton, and xenon. The element thatforms an oxygen vacancy is diffused from the insulating film 116 to thesource region 108 s and the drain region 108 d in the case where theinsulating film 116 contains one or more such elements. In addition oralternatively, the element that forms an oxygen vacancy is added to thesource region 108 s and the drain region 108 d by impurity additiontreatment.

An impurity element added to the oxide semiconductor film cuts a bondbetween a metal element and oxygen in the oxide semiconductor film, sothat an oxygen vacancy is formed. Alternatively, when an impurityelement is added to the oxide semiconductor film, oxygen bonded to ametal element in the oxide semiconductor film is bonded to the impurityelement and detached from the metal element, so that an oxygen vacancyis formed. As a result, the oxide semiconductor film has a highercarrier density, and thus, the conductivity thereof becomes higher.

Next, details of the components of the semiconductor device in FIGS. 29Ato 29C are described.

[Substrate]

As the substrate 102, any of a variety of substrates can be used withoutparticular limitation. The substrate 102 can be formed using a materialsimilar to that of the substrates 401, 452, 652, and 670 described inEmbodiment 1.

[First Insulating Film]

The insulating film 104 can be formed by a sputtering method, a CVDmethod, an evaporation method, a pulsed laser deposition (PLD) method, aprinting method, a coating method, or the like as appropriate. Forexample, the insulating film 104 can be formed to have a single-layerstructure or stacked-layer structure of an oxide insulating film and/ora nitride insulating film. To improve the properties of the interfacewith the oxide semiconductor film 108, at least a region of theinsulating film 104 which is in contact with the oxide semiconductorfilm 108 is preferably formed using an oxide insulating film. When theinsulating film 104 is formed using an oxide insulating film from whichoxygen is released by heating, oxygen contained in the insulating film104 can be moved to the oxide semiconductor film 108 by heat treatment.

The thickness of the insulating film 104 can be greater than or equal to50 nm, greater than or equal to 100 nm and less than or equal to 3000nm, or greater than or equal to 200 nm and less than or equal to 1000nm. By increasing the thickness of the insulating film 104, the amountof oxygen released from the insulating film 104 can be increased, andinterface states at the interface between the insulating film 104 andthe oxide semiconductor film 108 and oxygen vacancies included in thechannel region 108 i of the oxide semiconductor film 108 can be reduced.

For example, the insulating film 104 can be formed to have asingle-layer structure or stacked-layer structure of silicon oxide,silicon oxynitride, silicon nitride oxide, silicon nitride, aluminumoxide, hafnium oxide, gallium oxide, a Ga—Zn oxide, or the like. In thisembodiment, the insulating film 104 has a stacked-layer structure of asilicon nitride film and a silicon oxynitride film. With the insulatingfilm 104 having such a stack-layer structure including a silicon nitridefilm as a lower layer and a silicon oxynitride film as an upper layer,oxygen can be efficiently introduced into the oxide semiconductor film108.

[Oxide Semiconductor Film]

The oxide semiconductor film 108 can be formed using a material similarto that of the oxide semiconductor films 409 a, 409 b, and 409 cdescribed in Embodiment 1.

[Second Insulating Film]

The insulating film 110 functions as a gate insulating film of thetransistor 100. In addition, the insulating film 110 has a function ofsupplying oxygen to the oxide semiconductor film 108, particularly tothe channel region 108 i. The insulating film 110 can be formed to havea single-layer structure or a stacked-layer structure of an oxideinsulating film or a nitride insulating film, for example. To improvethe interface properties with the oxide semiconductor film 108, a regionwhich is in the insulating film 110 and in contact with the oxidesemiconductor film 108 is preferably formed using at least an oxideinsulating film. For example, silicon oxide, silicon oxynitride, siliconnitride oxide, or silicon nitride may be used for the insulating film110.

The thickness of the insulating film 110 can be greater than or equal to5 nm and less than or equal to 400 nm, greater than or equal to 5 nm andless than or equal to 300 nm, or greater than or equal to 10 nm and lessthan or equal to 250 nm.

It is preferable that the insulating film 110 have few defects andtypically have as few signals observed by electron spin resonance (ESR)spectroscopy as possible. Examples of the signals include a signal dueto an E′ center observed at a g-factor of 2.001. Note that the E′ centeris due to the dangling bond of silicon. As the insulating film 110, asilicon oxide film or a silicon oxynitride film whose spin density of asignal due to the E′ center is lower than or equal to 3×10¹⁷ spins/cm³and preferably lower than or equal to 5×10¹⁶ spins/cm³ may be used.

In addition to the above-described signal, a signal due to nitrogendioxide (NO₂) might be observed in the insulating film 110. The signalis divided into three signals according to the N nuclear spin; a firstsignal, a second signal, and a third signal. The first signal isobserved at a g-factor of greater than or equal to 2.037 and less thanor equal to 2.039. The second signal is observed at a g-factor ofgreater than or equal to 2.001 and less than or equal to 2.003. Thethird signal is observed at a g-factor of greater than or equal to 1.964and less than or equal to 1.966.

It is suitable to use an insulating film whose spin density of a signaldue to nitrogen dioxide (NO₂) is higher than or equal to 1×10¹⁷spins/cm³ and lower than 1×10¹⁸ spins/cm³ as the insulating film 110,for example.

Note that a nitrogen oxide (NO_(x)) such as a nitrogen dioxide (NO₂)forms a level in the insulating film 110. The level is positioned in theenergy gap of the oxide semiconductor film 108. Thus, when nitrogenoxide (NO_(x)) is diffused to the interface between the insulating film110 and the oxide semiconductor film 108, an electron might be trappedby the level on the insulating film 110 side. As a result, the trappedelectron remains in the vicinity of the interface between the insulatingfilm 110 and the oxide semiconductor film 108, leading to a positiveshift of the threshold voltage of the transistor. Accordingly, the useof a film with a low nitrogen oxide content as the insulating film 110can reduce a shift of the threshold voltage of the transistor.

As an insulating film that releases a small amount of nitrogen oxide(NO_(x)), for example, a silicon oxynitride film can be used. Thesilicon oxynitride film releases more ammonia than nitrogen oxide(NO_(x)) in thermal desorption spectroscopy (TDS); the typical releasedamount of ammonia is greater than or equal to 1×10¹⁸ molecules/cm³ andless than or equal to 5×10¹⁹ molecules/cm³. Note that the releasedamount of ammonia is the total amount of ammonia released by heattreatment in a range of 50° C. to 650° C. or 50° C. to 550° C. in TDS.

Since nitrogen oxide (NO)) reacts with ammonia and oxygen in heattreatment, the use of an insulating film that releases a large amount ofammonia reduces nitrogen oxide (NO_(x)).

Note that in the case where the insulating film 110 is analyzed by SIMS,nitrogen concentration in the film is preferably lower than or equal to6×10²⁰ atoms/cm³.

The insulating film 110 may be formed using a high-k material such ashafnium silicate (HfSiO_(x)), hafnium silicate to which nitrogen isadded (HfSi_(x)O_(y)N_(z)), hafnium aluminate to which nitrogen is added(HfAl_(x)O_(y)N_(z)), or hafnium oxide. The use of such a high-kmaterial enables a reduction in gate leakage current of a transistor.

[Third Insulating Film]

The insulating film 116 contains nitrogen or hydrogen. The insulatingfilm 116 may contain fluorine. As the insulating film 116, for example,a nitride insulating film can be used. The nitride insulating film canbe formed using silicon nitride, silicon nitride oxide, siliconoxynitride, silicon nitride fluoride, silicon fluoronitride, or thelike. The hydrogen concentration in the insulating film 116 ispreferably higher than or equal to 1×10²² atoms/cm³. Furthermore, theinsulating film 116 is in contact with the source region 108 s and thedrain region 108 d of the oxide semiconductor film 108. Thus, theconcentration of an impurity (nitrogen or hydrogen) in the source region108 s and the drain region 108 d in contact with the insulating film 116is increased, leading to an increase in the carrier density of thesource region 108 s and the drain region 108 d.

[Fourth Insulating Film]

As the insulating film 118, an oxide insulating film can be used.Alternatively, a stack including an oxide insulating film and a nitrideinsulating film can be used as the insulating film 118. The insulatingfilm 118 can be formed using, for example, silicon oxide, siliconoxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide,gallium oxide, or Ga—Zn oxide.

Furthermore, the insulating film 118 preferably functions as a barrierfilm against hydrogen, water, and the like from the outside.

The thickness of the insulating film 118 can be greater than or equal to30 nm and less than or equal to 500 nm, or greater than or equal to 100nm and less than or equal to 400 nm.

[Conductive Film]

The conductive films 112, 120 a, and 120 b can be formed by a sputteringmethod, a vacuum evaporation method, a pulsed laser deposition (PLD)method, a thermal CVD method, or the like. The conductive films 112, 120a, and 120 b can be formed using materials similar to those of theconductive films 402, 403 a, 403 b, 403 c, 405 a, 405 b, 405 c, 405 d,407 a, 407 b, 407 c, 407 d, 407 e, 411 a, 411 b, 411 c, 414 a, 414 b,414 c, 414 d, 414 e 414 f, 414 g, 414 h, 417, 420, and 608 which aredescribed in Embodiment 1.

The conductive films 112, 120 a, and 120 b can also be formed using alight-transmitting conductive material such as ITO, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, indium zinc oxide, or ITSO. It is also possible to havea layered structure formed using the above light-transmitting conductivematerial and the above metal element.

Note that an oxide semiconductor typified by an In—Ga—Zn oxide may beused for the conductive film 112. The oxide semiconductor can have ahigh carrier density when nitrogen or hydrogen is supplied from theinsulating film 116. In other words, the oxide semiconductor functionsas an oxide conductor (OC). Accordingly, the oxide semiconductor can beused for a gate electrode.

The conductive film 112 can have, for example, a single-layer structureof an oxide conductor (OC), a single-layer structure of a metal film, ora stacked-layer structure of an oxide conductor (OC) and a metal film.

Note that it is suitable that the conductive film 112 has a single-layerstructure of a light-shielding metal film or a stacked-layer structureof an oxide conductor (OC) and a light-shielding metal film because thechannel region 108 i formed under the conductive film 112 can beshielded from light. In the case where the conductive film 112 has astacked-layer structure of an oxide semiconductor or an oxide conductor(OC) and a light-shielding metal film, formation of a metal film (e.g.,a titanium film or a tungsten film) over the oxide semiconductor or theoxide conductor (OC) produces any of the following effects: theresistance of the oxide semiconductor or the oxide conductor (OC) isreduced by the diffusion of the constituent element of the metal film tothe oxide semiconductor or oxide conductor (OC) side, the resistance isreduced by damage (e.g., sputtering damage) during the deposition of themetal film, and the resistance is reduced when oxygen vacancies areformed by the diffusion of oxygen in the oxide semiconductor or theoxide conductor (OC) to the metal film.

The thickness of the conductive films 112, 120 a, and 120 b can begreater than or equal to 30 nm and less than or equal to 500 nm, orgreater than or equal to 100 nm and less than or equal to 400 nm.

<3-2. Structure Example 2 of Semiconductor Device>

Next, a structure of a transistor different from that in FIGS. 29A to29C is described with reference to FIGS. 30A to 30C.

FIG. 30A is a top view of a transistor 100A. FIG. 30B is across-sectional view taken along the dashed-dotted line X1-X2 in FIG.30A. FIG. 30C is a cross-sectional view taken along the dashed-dottedline Y1-Y2 in FIG. 30A.

The transistor 100A illustrated in FIGS. 30A to 30C includes aconductive film 106 over the substrate 102; the insulating film 104 overthe conductive film 106; the oxide semiconductor film 108 over theinsulating film 104; the insulating film 110 over the oxidesemiconductor film 108; the conductive film 112 over the insulating film110; and the insulating film 116 over the insulating film 104, the oxidesemiconductor film 108, and the conductive film 112. Note that the oxidesemiconductor film 108 includes the channel region 108 i overlappingwith the conductive film 112, the source region 108 s in contact withthe insulating film 116, and the drain region 108 d in contact with theinsulating film 116.

The transistor 100A includes the conductive film 106 and an opening 143in addition to the components of the transistor 100 described above.

Note that the opening 143 is provided in the insulating films 104 and110. The conductive film 106 is electrically connected to the conductivefilm 112 through the opening 143. Thus, the same potential is applied tothe conductive film 106 and the conductive film 112. Note that differentpotentials may be applied to the conductive film 106 and the conductivefilm 112 without providing the opening 143. Alternatively, theconductive film 106 may be used as a light-shielding film withoutproviding the opening 143. When the conductive film 106 is formed usinga light-shielding material, for example, light irradiating the channelregion 108 i from the bottom can be reduced.

In the case of the structure of the transistor 100A, the conductive film106 functions as a first gate electrode (also referred to as abottom-gate electrode), the conductive film 112 functions as a secondgate electrode (also referred to as a top-gate electrode), theinsulating film 104 functions as a first gate insulating film, and theinsulating film 110 functions as a second gate insulating film.

The conductive film 106 can be formed using a material similar to theabove-described materials of the conductive films 112, 120 a, and 120 b.It is particularly suitable to use a material containing copper for theconductive film 106 because the resistance can be reduced. It issuitable that, for example, each of the conductive films 106, 120 a, and120 b has a stacked-layer structure in which a copper film is over atitanium nitride film, a tantalum nitride film, or a tungsten film. Inthat case, when the transistor 100A is used as a pixel transistor and/ora driving transistor of a display device, parasitic capacitancegenerated between the conductive films 106 and 120 a and between theconductive films 106 and 120 b can be reduced. Thus, the conductivefilms 106, 120 a, and 120 b can be used not only as the first gateelectrode, the source electrode, and the drain electrode of thetransistor 100A, but also as power source supply wirings, signal supplywirings, connection wirings, or the like of the display device.

In this manner, unlike the transistor 100 described above, thetransistor 100A in FIGS. 30A to 30C has a structure in which aconductive film functioning as a gate electrode is provided over andunder the oxide semiconductor film 108. As in the transistor 100A, asemiconductor device of one embodiment of the present invention may havea plurality of gate electrodes.

As illustrated in FIG. 30C, the oxide semiconductor film 108 faces theconductive film 106 functioning as a first gate electrode and theconductive film 112 functioning as a second gate electrode and ispositioned between the two conductive films functioning as the gateelectrodes.

Furthermore, the length of the conductive film 112 in the channel widthdirection is larger than the length of the oxide semiconductor film 108in the channel width direction. In the channel width direction, thewhole oxide semiconductor film 108 is covered with the conductive film112 with the insulating film 110 placed therebetween. Since theconductive film 112 is connected to the conductive film 106 through theopening 143 provided in the insulating films 104 and 110, a side surfaceof the oxide semiconductor film 108 in the channel width direction facesthe conductive film 112 with the insulating film 110 placedtherebetween.

In other words, in the channel width direction of the transistor 100A,the conductive films 106 and 112 are connected to each other through theopening 143 provided in the insulating films 104 and 110, and theconductive films 106 and 112 surround the oxide semiconductor film 108with the insulating films 104 and 110 placed therebetween.

Such a structure enables the oxide semiconductor film 108 included inthe transistor 100A to be electrically surrounded by electric fields ofthe conductive film 106 functioning as a first gate electrode and theconductive film 112 functioning as a second gate electrode. A devicestructure of a transistor, like that of the transistor 100A, in whichelectric fields of a first gate electrode and a second gate electrodeelectrically surround an oxide semiconductor film in which a channelregion is formed can be referred to as a surrounded channel (S-channel)structure.

Since the transistor 100A has the S-channel structure, an electric fieldfor inducing a channel can be effectively applied to the oxidesemiconductor film 108 by the conductive film 106 or the conductive film112; thus, the current drive capability of the transistor 100A can beimproved and high on-state current characteristics can be obtained. As aresult of the high on-state current, it is possible to reduce the sizeof the transistor 100A. Furthermore, since the transistor 100A has astructure in which the oxide semiconductor film 108 is surrounded by theconductive film 106 and the conductive film 112, the mechanical strengthof the transistor 100A can be increased.

When seen in the channel width direction of the transistor 100A, anopening different from the opening 143 may be formed on the side of theoxide semiconductor film 108 on which the opening 143 is not formed.

When a transistor has a pair of gate electrodes between which asemiconductor film is positioned as in the transistor 100A, one of thegate electrodes may be supplied with a signal A, and the other gateelectrode may be supplied with a fixed potential V_(b). Alternatively,one of the gate electrodes may be supplied with the signal A, and theother gate electrode may be supplied with a signal B. Alternatively, oneof the gate electrodes may be supplied with a fixed potential V_(a), andthe other gate electrode may be supplied with the fixed potential V_(b).

The signal A is, for example, a signal for controlling the on/off state.The signal A may be a digital signal with two kinds of potentials, apotential V1 and a potential V2 (V1>V2). For example, the potential V1can be a high power supply potential, and the potential V2 can be a lowpower supply potential. The signal A may be an analog signal.

The fixed potential V_(b) is, for example, a potential for controlling athreshold voltage V_(thA) of the transistor. The fixed potential V_(b)may be the potential V1 or the potential V2. In that case, a potentialgenerator circuit for generating the fixed potential V_(b) is notnecessary, which is preferable. The fixed potential V_(b) may bedifferent from the potential V1 or the potential V2. When the fixedpotential V_(b) is low, the threshold voltage V_(thA) can be high insome cases. As a result, the drain current flowing when the gate-sourcevoltage V_(gs) is 0 V can be reduced, and leakage current in a circuitincluding the transistor can be reduced in some cases. The fixedpotential V_(b) may be, for example, lower than the low power supplypotential. Meanwhile, a high fixed potential V_(b) can lower thethreshold voltage V_(thA) in some cases. As a result, the drain currentflowing when the gate-source voltage V_(gs) is a high power supplypotential and the operating speed of the circuit including thetransistor can be increased in some cases. The fixed potential V_(b) maybe, for example, higher than the low power supply potential.

The signal B is, for example, a signal for controlling the on/off state.The signal B may be a digital signal with two kinds of potentials, apotential V3 and a potential V4 (V3>V4). For example, the potential V3can be a high power supply potential, and the potential V4 can be a lowpower supply potential. The signal B may be an analog signal.

When both the signal A and the signal B are digital signals, the signalB may have the same digital value as the signal A. In this case, it maybe possible to increase the on-state current of the transistor and theoperating speed of the circuit including the transistor. Here, thepotential V1 and the potential V2 of the signal A may be different fromthe potential V3 and the potential V4 of the signal B. For example, if agate insulating film for the gate to which the signal B is input isthicker than a gate insulating film for the gate to which the signal Ais input, the potential amplitude of the signal B (V3−V4) may be largerthan the potential amplitude of the signal A (V1−V2). In this manner,the influence of the signal A and that of the signal B on the on/offstate of the transistor can be substantially the same in some cases.

When both the signal A and the signal B are digital signals, the signalB may have a digital value different from that of the signal A. In thiscase, the signal A and the signal B can separately control thetransistor, and thus, higher performance can be achieved. The transistorwhich is, for example, an n-channel transistor can function by itself asa NAND circuit, a NOR circuit, or the like in the following case: thetransistor is turned on only when the signal A has the potential V1 andthe signal B has the potential V3, or the transistor is turned off onlywhen the signal A has the potential V2 and the signal B has thepotential V4. The signal B may be a signal for controlling the thresholdvoltage V_(thA). For example, the potential of the signal B in a periodin which the circuit including the transistor operates may be differentfrom the potential of the signal B in a period in which the circuit doesnot operate. The potential of the signal B may vary depending on theoperation mode of the circuit. In this case, the potential of the signalB is not changed as frequently as the potential of the signal A in somecases.

When both the signal A and the signal B are analog signals, the signal Bmay be an analog signal having the same potential as the signal A, ananalog signal whose potential is a constant times the potential of thesignal A, an analog signal whose potential is higher or lower than thepotential of the signal A by a constant, or the like. In this case, itmay be possible to increase the on-state current of the transistor andthe operating speed of the circuit including the transistor. The signalB may be an analog signal different from the signal A. In this case, thesignal A and the signal B can separately control the transistor, andthus, higher performance can be achieved.

The signal A may be a digital signal, and the signal B may be an analogsignal. Alternatively, the signal A may be an analog signal, and thesignal B may be a digital signal.

When both of the gate electrodes of the transistor are supplied with thefixed potentials, the transistor can function as an element equivalentto a resistor in some cases. For example, in the case where thetransistor is an n-channel transistor, the effective resistance of thetransistor can be sometimes low (high) when the fixed potential V_(a) orthe fixed potential V_(b) is high (low). When both the fixed potentialV_(a) and the fixed potential V_(b) are high (low), the effectiveresistance can be lower (higher) than that of a transistor with only onegate in some cases.

Except for the above-mentioned points, the transistor 100A has astructure and an effect similar to those of the transistor 100 describedabove.

<3-3. Structure Example 3 of Transistor>

Next, structures of a transistor different from that in FIGS. 30A to 30Care described with reference to FIGS. 31A and 31B, FIGS. 32A and 32B,FIGS. 33A and 33B, FIGS. 34A and 34B, FIGS. 35A and 35B, and FIGS. 36Ato 36C.

FIGS. 31A and 31B are cross-sectional views of a transistor 100F. FIGS.32A and 32B are cross-sectional views of a transistor 100G. FIGS. 33Aand 33B are cross-sectional views of a transistor 100H. FIGS. 34A and34B are cross-sectional views of a transistor 100J. FIGS. 35A and 35Bare cross-sectional views of a transistor 100K. Note that top views ofthe transistor 100F, the transistor 100G, the transistor 100H, thetransistor 100J, and the transistor 100K are similar to that of thetransistor 100A illustrated in FIG. 30A and thus are not described here.

The transistors 100F, 100G, 100H, 100J, and 100K are different from theabove-described transistor 100A in the structure of the oxidesemiconductor film 108. The other components of the transistors aresimilar to those of the transistor 100A described above and have similareffects.

The oxide semiconductor film 108 of the transistor 100F illustrated inFIGS. 31A and 31B includes an oxide semiconductor film 108_1 over theinsulating film 104, an oxide semiconductor film 108_2 over the oxidesemiconductor film 108_1, and an oxide semiconductor film 108_3 over theoxide semiconductor film 108_2. The channel region 108 i, the sourceregion 108 s, and the drain region 108 d each have a three-layerstructure of the oxide semiconductor film 108_1, the oxide semiconductorfilm 108_2, and the oxide semiconductor film 108_3.

The oxide semiconductor film 108 of the transistor 100G illustrated inFIGS. 32A and 32B includes the oxide semiconductor film 108_2 over theinsulating film 104, and the oxide semiconductor film 108_3 over theoxide semiconductor film 108_2. The channel region 108 i, the sourceregion 108 s, and the drain region 108 d each have a two-layer structureof the oxide semiconductor film 108_2 and the oxide semiconductor film108_3.

The oxide semiconductor film 108 of the transistor 100H illustrated inFIGS. 33A and 33B includes the oxide semiconductor film 108_1 over theinsulating film 104, and the oxide semiconductor film 108_2 over theoxide semiconductor film 108_1. The channel region 108 i, the sourceregion 108 s, and the drain region 108 d each have a two-layer structureof the oxide semiconductor film 108_1 and the oxide semiconductor film108_2.

The oxide semiconductor film 108 of the transistor 100J illustrated inFIGS. 34A and 34B includes the oxide semiconductor film 108_1 over theinsulating film 104, the oxide semiconductor film 108_2 over the oxidesemiconductor film 108_1, and the oxide semiconductor film 108_3 overthe oxide semiconductor film 108_2. The channel region 108 i has athree-layer structure of the oxide semiconductor film 108_1, the oxidesemiconductor film 108_2, and the oxide semiconductor film 108_3. Thesource region 108 s and the drain region 108 d each have a two-layerstructure of the oxide semiconductor film 108_1 and the oxidesemiconductor film 108_2. Note that in the cross section of thetransistor 100J in the channel width (W) direction, the oxidesemiconductor film 108_3 covers side surfaces of the oxide semiconductorfilm 108_1 and the oxide semiconductor film 108_2.

The oxide semiconductor film 108 of the transistor 100K illustrated inFIGS. 35A and 35B includes the oxide semiconductor film 108_2 over theinsulating film 104, and the oxide semiconductor film 108_3 over theoxide semiconductor film 108_2. The channel region 108 i has a two-layerstructure of the oxide semiconductor film 108_2 and the oxidesemiconductor film 108_3. The source region 108 s and the drain region108 d each have a single-layer structure of the oxide semiconductor film108_2. Note that in the cross section of the transistor 100K in thechannel width (W) direction, the oxide semiconductor film 108_3 coversside surfaces of the oxide semiconductor film 108_2.

A side surface of the channel region 108 i in the channel width (W)direction or a region in the vicinity of the side surface is easilydamaged by processing, resulting in a defect (e.g., oxygen vacancy), oreasily contaminated by an impurity attached thereto. Therefore, evenwhen the channel region 108 i is substantially intrinsic, stress such asan electric field applied thereto activates the side surface of thechannel region 108 i in the channel width (W) direction or the region inthe vicinity of the side surface and turns it into a low-resistance(n-type) region easily. Moreover, if the side surface of the channelregion 108 i in the channel width (W) direction or the region in thevicinity of the side surface is an n-type region, a parasitic channelmay be formed because the n-type region serves as a carrier path.

Thus, in the transistor 100J and the transistor 100K, the channel region108 i has a stacked-layer structure and side surfaces of the channelregion 108 i in the channel width (W) direction are covered with onelayer of the stacked layers. With such a structure, defects on or in thevicinity of the side surfaces of the channel region 108 i can besuppressed or adhesion of an impurity to the side surfaces of thechannel region 108 i or to regions in the vicinity of the side surfacescan be reduced.

<3-4. Band Structure>

Here, a band structure of the insulating film 104, the oxidesemiconductor films 108_1, 108_2, and 108_3, and the insulating film110, a band structure of the insulating film 104, the oxidesemiconductor films 108_2 and 108_3, and the insulating film 110, and aband structure of the insulating film 104, the oxide semiconductor films108_1 and 108_2, and the insulating film 110 are described withreference to FIGS. 36A to 36C. Note that FIGS. 36A to 36C are each aband structure of the channel region 108 i.

FIG. 36A shows an example of a band structure in the thickness directionof a stack including the insulating film 104, the oxide semiconductorfilms 108_1, 108_2, and 108_3, and the insulating film 110. FIG. 36Bshows an example of a band structure in the thickness direction of astack including the insulating film 104, the oxide semiconductor films108_2 and 108_3, and the insulating film 110. FIG. 36C shows an exampleof a band structure in the thickness direction of a stack including theinsulating film 104, the oxide semiconductor films 108_1 and 108_2, andthe insulating film 110. For easy understanding, the band structuresshow the conduction band minimum (E_(c)) of the insulating film 104, theoxide semiconductor films 108_1, 108_2, and 108_3, and the insulatingfilm 110.

In the band structure of FIG. 36A, a silicon oxide film is used as eachof the insulating films 104 and 110, an oxide semiconductor film formedusing a metal oxide target whose atomic ratio of In to Ga and Zn is1:3:2 is used as the oxide semiconductor film 108_1, an oxidesemiconductor film formed using a metal oxide target whose atomic ratioof In to Ga and Zn is 4:2:4.1 is used as the oxide semiconductor film108_2, and an oxide semiconductor film formed using a metal oxide targetwhose atomic ratio of In to Ga and Zn is 1:3:2 is used as the oxidesemiconductor film 108_3.

In the band structure of FIG. 36B, a silicon oxide film is used as eachof the insulating films 104 and 110, an oxide semiconductor film formedusing a metal oxide target whose atomic ratio of In to Ga and Zn is4:2:4.1 is used as the oxide semiconductor film 108_2, and an oxidesemiconductor film formed using a metal oxide target whose atomic ratioof In to Ga and Zn is 1:3:2 is used as the oxide semiconductor film108_3.

In the band structure of FIG. 36C, a silicon oxide film is used as eachof the insulating films 104 and 110, an oxide semiconductor film formedusing a metal oxide target whose atomic ratio of In to Ga and Zn is1:3:2 is used as the oxide semiconductor film 108_1, and an oxidesemiconductor film formed using a metal oxide target whose atomic ratioof In to Ga and Zn is 4:2:4.1 is used as the oxide semiconductor film108_2.

As illustrated in FIG. 36A, the conduction band minimum gradually variesbetween the oxide semiconductor films 108_1, 108_2, and 108_3. Asillustrated in FIG. 36B, the conduction band minimum gradually variesbetween the oxide semiconductor films 108_2 and 108_3. As illustrated inFIG. 36C, the conduction band minimum gradually varies between the oxidesemiconductor films 108_1 and 108_2. In other words, the conduction bandminimum is continuously changed or continuously connected. To obtainsuch a band structure, there exists no impurity, which forms a defectstate such as a trap center or a recombination center, at the interfacebetween the oxide semiconductor films 108_1 and 108_2 or the interfacebetween the oxide semiconductor films 108_2 and 108_3.

To form a continuous junction between the oxide semiconductor films108_1, 108_2, and 108_3, it is necessary to form the films successivelywithout exposure to the air with a multi-chamber deposition apparatus(sputtering apparatus) provided with a load lock chamber.

With the band structure of FIG. 36A, FIG. 36B, or FIG. 36C, the oxidesemiconductor film 108_2 serves as a well, and a channel region isformed in the oxide semiconductor film 108_2 in the transistor with thestacked-layer structure.

By providing the oxide semiconductor films 108_1 and 108_3, the oxidesemiconductor film 108_2 can be distanced away from trap states.

In addition, the trap states might be more distant from the vacuum levelthan the conduction band minimum (E_(c)) of the oxide semiconductor film108_2 functioning as a channel region, so that electrons are likely tobe accumulated in the trap states. When the electrons are accumulated inthe trap states, the electrons become negative fixed electric charge, sothat the threshold voltage of the transistor is shifted in the positivedirection. Therefore, it is preferable that the trap states be closer tothe vacuum level than the conduction band minimum (E_(c)) of the oxidesemiconductor film 108_2. Such a structure inhibits accumulation ofelectrons in the trap states. As a result, the on-state current and thefield-effect mobility of the transistor can be increased.

The conduction band minimum of each of the oxide semiconductor films108_1 and 108_3 is closer to the vacuum level than that of the oxidesemiconductor film 108_2. A typical difference between the conductionband minimum of the oxide semiconductor film 108_2 and the conductionband minimum of each of the oxide semiconductor films 108_1 and 108_3 is0.15 eV or more or 0.5 eV or more and 2 eV or less or 1 eV or less. Thatis, the difference between the electron affinity of each of the oxidesemiconductor films 108_1 and 108_3 and the electron affinity of theoxide semiconductor film 108_2 is 0.15 eV or more or 0.5 eV or more and2 eV or less or 1 eV or less.

In such a structure, the oxide semiconductor film 108_2 serves as a mainpath of a current. In other words, the oxide semiconductor film 108_2serves as a channel region, and the oxide semiconductor films 108_1 and108_3 function as oxide insulating films. It is preferable that theoxide semiconductor films 108_1 and 108_3 each include one or more metalelements constituting a part of the oxide semiconductor film 108_2 inwhich a channel region is formed. With such a structure, interfacescattering hardly occurs at the interface between the oxidesemiconductor film 108_1 and the oxide semiconductor film 108_2 or atthe interface between the oxide semiconductor film 108_2 and the oxidesemiconductor film 108_3. Thus, the transistor can have highfield-effect mobility because the movement of carriers is not hinderedat the interface.

To prevent each of the oxide semiconductor films 108_1 and 108_3 fromfunctioning as part of a channel region, a material having sufficientlylow conductivity is used for the oxide semiconductor films 108_1 and108_3. Thus, the oxide semiconductor films 108_1 and 108_3 can bereferred to as oxide insulating films for such properties and/orfunctions. Alternatively, a material that has a smaller electronaffinity (a difference between the vacuum level and the conduction bandminimum) than the oxide semiconductor film 108_2 and has a difference inthe conduction band minimum from the oxide semiconductor film 108_2(band offset) is used for the oxide semiconductor films 108_1 and 108_3.Furthermore, to inhibit generation of a difference in threshold voltagedue to the value of the drain voltage, it is preferable to form theoxide semiconductor films 108_1 and 108_3 using a material whoseconduction band minimum is closer to the vacuum level than that of theoxide semiconductor film 108_2. For example, a difference between theconduction band minimum of the oxide semiconductor film 108_2 and theconduction band minimum of each of the oxide semiconductor films 108_1and 108_3 is preferably greater than or equal to 0.2 eV, more preferablygreater than or equal to 0.5 eV.

It is preferable that the oxide semiconductor films 108_1 and 108_3 nothave a spinel crystal structure. This is because if the oxidesemiconductor films 108_1 and 108_3 have a spinel crystal structure,constituent elements of the conductive films 120 a and 120 b might bediffused into the oxide semiconductor film 108_2 at the interfacebetween the spinel crystal structure and another region. Note that eachof the oxide semiconductor films 108_1 and 108_3 is preferably a CAAC-OSfilm described later, in which case a higher blocking property againstconstituent elements of the conductive films 120 a and 120 b, forexample, copper elements, can be obtained.

Although the example where an oxide semiconductor film formed using ametal oxide target whose atomic ratio of In to Ga and Zn is 1:3:2, isused as each of the oxide semiconductor films 108_1 and 108_3 isdescribed in this embodiment, one embodiment of the present invention isnot limited thereto. For example, an oxide semiconductor film formedusing a metal oxide target whose atomic ratio of In to Ga and Zn is1:1:1, 1:1:1.2, 1:3:4, 1:3:6, 1:4:5, 1:5:6, or 1:10:1 may be used aseach of the oxide semiconductor films 108_1 and 108_3. Alternatively,oxide semiconductor films formed using a metal oxide target whose atomicratio of Ga to Zn is 10:1 may be used as the oxide semiconductor films108_1 and 108_3. In that case, it is suitable that an oxidesemiconductor film formed using a metal oxide target whose atomic ratioof In to Ga and Zn is 1:1:1 is used as the oxide semiconductor film108_2 because the difference between the conduction band minimum of theoxide semiconductor film 108_2 and the conduction band minimum of theoxide semiconductor film 108_1 or 108_3 can be 0.6 eV or more.

When the oxide semiconductor films 108_1 and 108_3 are formed using ametal oxide target whose atomic ratio of In to Ga and Zn is 1:1:1, theatomic ratio of In to Ga and Zn in the oxide semiconductor films 108_1and 108_3 might be 1:β1:β2 (0<β1≦2, 0<β2≦2). When the oxidesemiconductor films 108_1 and 108_3 are formed using a metal oxidetarget whose atomic ratio of In to Ga and Zn is 1:3:4, the atomic ratioof In to Ga and Zn in the oxide semiconductor films 108_1 and 108_3might be 1:β3:β4 (1≦β3≦5, 2≦4≦6). When the oxide semiconductor films108_1 and 108_3 are formed using a metal oxide target whose atomic ratioof In to Ga and Zn is 1:3:6, the atomic ratio of In to Ga and Zn in theoxide semiconductor films 108_1 and 108_3 might be 1:β5:β6 (1≦β5,4≦β6≦8).

The structure and method described in this embodiment can be used inappropriate combination with with any of the other structures andmethods described in the other embodiments.

Embodiment 4

In this embodiment, a transistor that can be used for the display deviceof one embodiment of the present invention is described in detail.

In this embodiment, an inverted staggered transistor is described withreference to FIGS. 37A to 37C, FIGS. 38A to 38C, FIGS. 39A to 39C, FIGS.40A to 40C, and FIGS. 41A to 41D.

<4-1. Structure Example 1 of Transistor>

FIG. 37A is a top view of a transistor 300A. FIG. 37B is across-sectional view taken along dashed-dotted line X1-X2 in FIG. 37A.FIG. 37C is a cross-sectional view taken along dashed-dotted line Y1-Y2in FIG. 37A. Note that in FIG. 37A, some components of the transistor300A (e.g., an insulating film functioning as a gate insulating film)are not illustrated to avoid complexity. The direction of dashed-dottedline X1-X2 may be referred to as a channel length direction, and thedirection of dashed-dotted line Y1-Y2 may be referred to as a channelwidth direction. As in FIG. 37A, some components are not illustrated insome cases in top views of transistors described below.

The transistor 300A includes a conductive film 304 functioning as a gateelectrode over a substrate 302, an insulating film 306 over thesubstrate 302 and the conductive film 304, an insulating film 307 overthe insulating film 306, an oxide semiconductor film 308 over theinsulating film 307, a conductive film 312 a functioning as a sourceelectrode electrically connected to the oxide semiconductor film 308,and a conductive film 312 b functioning as a drain electrodeelectrically connected to the oxide semiconductor film 308. Over thetransistor 300A, specifically, over the conductive films 312 a and 312 band the oxide semiconductor film 308, an insulating film 314, aninsulating film 316, and an insulating film 318 are provided. Theinsulating films 314, 316, and 318 function as a protective insulatingfilm for the transistor 300A.

<4-2. Structure Example 2 of Transistor>

FIG. 38A is a top view of a transistor 300B. FIG. 38B is across-sectional view taken along dashed-dotted line X1-X2 in FIG. 38A.FIG. 38C is a cross-sectional view taken along dashed-dotted line Y1-Y2in FIG. 38A.

The transistor 300B includes the conductive film 304 functioning as agate electrode over the substrate 302, the insulating film 306 over thesubstrate 302 and the conductive film 304, the insulating film 307 overthe insulating film 306, the oxide semiconductor film 308 over theinsulating film 307, the insulating film 314 over the oxidesemiconductor film 308, the insulating film 316 over the insulating film314, the conductive film 312 a functioning as a source electrode, andthe conductive film 312 b functioning as a drain electrode. Theconductive film 312 a is electrically connected to the oxidesemiconductor film 308 through an opening 341 a provided in theinsulating films 314 and 316. The conductive film 312 b is electricallyconnected to the oxide semiconductor film 308 through an opening 341 bprovided in the insulating films 314 and 316. Over the transistor 300B,specifically, over the conductive films 312 a and 312 b and theinsulating film 316, the insulating film 318 is provided. The insulatingfilms 314 and 316 function as a protective insulating film for the oxidesemiconductor film 308. The insulating film 318 functions as aprotective insulating film for the transistor 300B.

The transistor 300A has a channel-etched structure, whereas thetransistor 300B in FIGS. 38A to 38C has a channel-protective structure.

<4-3. Structure Example 3 of Transistor>

FIG. 39A is a top view of a transistor 300C. FIG. 39B is across-sectional view taken along dashed-dotted line X1-X2 in FIG. 39A.FIG. 39C is a cross-sectional view taken along dashed-dotted line Y1-Y2in FIG. 39A.

The transistor 300C is different from the transistor 300B in FIGS. 38Ato 38C in the shapes of the insulating films 314 and 316. Specifically,the insulating films 314 and 316 of the transistor 300C have islandshapes and are provided over a channel region of the oxide semiconductorfilm 308. Other components are similar to those of the transistor 300B.

<4-4. Structure Example 4 of Transistor>

FIG. 40A is a top view of a transistor 300D. FIG. 40B is across-sectional view taken along dashed-dotted line X1-X2 in FIG. 40A.FIG. 40C is a cross-sectional view taken along dashed-dotted line Y1-Y2in FIG. 40A.

The transistor 300D includes the conductive film 304 functioning as afirst gate electrode over the substrate 302, the insulating film 306over the substrate 302 and the conductive film 304, the insulating film307 over the insulating film 306, the oxide semiconductor film 308 overthe insulating film 307, the insulating film 314 over the oxidesemiconductor film 308, the insulating film 316 over the insulating film314, the conductive film 312 a functioning as a source electrode, theconductive film 312 b functioning as a drain electrode, the insulatingfilm 318 over the conductive films 312 a and 312 b and the insulatingfilm 316, and a conductive film 320 a and a conductive film 320 b overthe insulating film 318. The conductive films 312 a and 312 b areelectrically connected to the oxide semiconductor film 308.

In the transistor 300D, the insulating films 314, 316, and 318 functionas a second gate insulating film of the transistor 300D. Furthermore,the conductive film 320 a in the transistor 300D functions as a pixelelectrode used for the display device. The conductive film 320 a isconnected to the conductive film 312 b through an opening 342 c providedin the insulating films 314, 316, and 318. In the transistor 300D, theconductive film 320 b functions as a second gate electrode (alsoreferred to as a back gate electrode).

As illustrated in FIG. 40C, the conductive film 320 b is connected tothe conductive film 304, which functions as the first gate electrode, inan opening 342 a and an opening 342 b provided in the insulating films306, 307, 314, 316, and 318. Thus, the same potential is applied to theconductive film 320 b and the conductive film 304.

The structure of the transistor 300D is not limited to that describedabove, in which the openings 342 a and 342 b are provided so that theconductive film 320 b is connected to the conductive film 304. Forexample, a structure in which only one of the openings 342 a and 342 bis provided so that the conductive film 320 b is connected to theconductive film 304, or a structure in which the conductive film 320 bis not connected to the conductive film 304 without providing theopenings 342 a and 342 b may be employed. Note that in the case wherethe conductive film 320 b is not connected to the conductive film 304,it is possible to apply different potentials to the conductive film 320b and the conductive film 304.

Note that the transistor 300D has the s-channel structure describedabove.

<4-5. Structure Example 5 of Transistor>

The oxide semiconductor film 308 included in the transistor 300A inFIGS. 37A to 37C may have a stacked-layer structure. FIGS. 41A to 41Dillustrate examples of such a case.

FIGS. 41A and 41B are cross-sectional views of a transistor 300E andFIGS. 41C and 41D are cross-sectional views of a transistor 300F. Thetop views of the transistors 300E and 300F are similar to that of thetransistor 300A illustrated in FIG. 37A.

The oxide semiconductor film 308 of the transistor 300E illustrated inFIGS. 41A and 41B includes an oxide semiconductor film 308_1, an oxidesemiconductor film 308_2, and an oxide semiconductor film 308_3. Theoxide semiconductor film 308 of the transistor 300F illustrated in FIGS.41C and 41D includes the oxide semiconductor film 308_2 and the oxidesemiconductor film 308_3.

Note that the conductive film 304, the insulating film 306, theinsulating film 307, the oxide semiconductor film 308, the oxidesemiconductor film 308_1, the oxide semiconductor film 308_2, the oxidesemiconductor film 308_3, the conductive film 312 a, the conductive film312 b, the insulating film 314, the insulating film 316, the insulatingfilm 318, and the conductive films 320 a and 320 b can be formed usingthe materials and formation methods of the conductive film 106, theinsulating film 116, the insulating film 314, the oxide semiconductorfilm 108, the oxide semiconductor film 108_1, the oxide semiconductorfilm 108_2, the oxide semiconductor film 108_3, the conductive film 120a, the conductive film 120 b, the insulating film 104, the insulatingfilm 118, the insulating film 116, and the conductive film 112 describedin Embodiment 3.

The structures of the transistors 300A to 300F can be freely combinedwith each other.

The structure described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, the structure and the like of an oxide semiconductorare described with reference to FIGS. 42A to 42E, FIGS. 43A to 43E,FIGS. 44A to 44D, FIGS. 45A and 45B, and FIG. 46.

<5-1. Structure of Oxide Semiconductor>

An oxide semiconductor is classified into a single-crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofthe non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a nanocrystalline oxide semiconductor (nc-OS), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

From another perspective, an oxide semiconductor is classified into anamorphous oxide semiconductor and a crystalline oxide semiconductor.Examples of the crystalline oxide semiconductor include a single-crystaloxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor,and an nc-OS.

An amorphous structure is generally thought to be isotropic and have nonon-uniform structure, to be metastable and have no fixed atomicarrangement, to have a flexible bond angle, and to have a short-rangeorder but have no long-range order, for example.

In other words, a stable oxide semiconductor cannot be regarded as acompletely amorphous oxide semiconductor. Moreover, an oxidesemiconductor that is not isotropic (e.g., an oxide semiconductor thathas a periodic structure in a microscopic region) cannot be regarded asa completely amorphous oxide semiconductor. In contrast, an a-like OS,which is not isotropic, has an unstable structure that contains a void.Because of its instability, an a-like OS has physical properties similarto those of an amorphous oxide semiconductor.

<5-2. CAAC-OS>

First, a CAAC-OS is described.

A CAAC-OS is one of oxide semiconductors and has a plurality of c-axisaligned crystal parts (also referred to as pellets).

Analysis of a CAAC-OS by X-ray diffraction (XRD) is described. Forexample, when the structure of a CAAC-OS including an InGaZnO₄ crystal,which is classified into the space group R-3m, is analyzed by anout-of-plane method, a peak appears at a diffraction angle (2θ) ofaround 31° as shown in FIG. 42A. This peak is derived from the (009)plane of the InGaZnO₄ crystal, which indicates that crystals in theCAAC-OS have c-axis alignment and that the c-axes are aligned in thedirection substantially perpendicular to a surface over which theCAAC-OS is formed (also referred to as a formation surface) or a topsurface of the CAAC-OS. Note that a peak sometimes appears at 2θ ofaround 36° in addition to the peak at 2θ of around 31°. The peak at 2θof around 36° is attributed to a crystal structure classified into thespace group Fd-3m; thus, this peak is preferably not exhibited in theCAAC-OS.

On the other hand, in structural analysis of the CAAC-OS by an in-planemethod in which an X-ray is incident on the CAAC-OS in the directionparallel to the formation surface, a peak appears at 2θ of around 56°.This peak is derived from the (110) plane of the InGaZnO₄ crystal. Whenanalysis (φ scan) is performed with 2θ fixed at around 56° while thesample is rotated around a normal vector to the sample surface as anaxis (φ axis), as shown in FIG. 42B, a peak is not clearly observed. Incontrast, in the case where single-crystal InGaZnO₄ is subjected to φscan with 2θ fixed at around 56°, as shown in FIG. 42C, six peaks whichare derived from crystal planes equivalent to the (110) plane areobserved. Accordingly, the structural analysis using XRD shows that thedirections of the a-axes and b-axes are irregularly oriented in theCAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction is described. Forexample, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in the directionparallel to the formation surface of the CAAC-OS, a diffraction pattern(also referred to as a selected-area electron diffraction pattern) inFIG. 42D can be obtained. This diffraction pattern includes spotsderived from the (009) plane of the InGaZnO₄ crystal. Thus, the resultsof electron diffraction also indicate that pellets included in theCAAC-OS have c-axis alignment and that the c-axes are aligned in thedirection substantially perpendicular to the formation surface or thetop surface of the CAAC-OS. Meanwhile, FIG. 42E shows a diffractionpattern obtained in such a manner that an electron beam with a probediameter of 300 nm is incident on the same sample in the directionperpendicular to the sample surface. In FIG. 42E, a ring-likediffraction pattern is observed. Thus, the results of electrondiffraction using an electron beam with a probe diameter of 300 nm alsoindicate that the a-axes and b-axes of the pellets included in theCAAC-OS do not have regular alignment. The first ring in FIG. 42E isderived from the (010) plane, the (100) plane, and the like of theInGaZnO₄ crystal. The second ring in FIG. 42E is derived from the (110)plane and the like.

In a combined analysis image (also referred to as a high-resolutiontransmission electron microscope (TEM) image) of a bright-field imageand a diffraction pattern of a CAAC-OS, which is obtained using a TEM, aplurality of pellets can be observed. However, even in thehigh-resolution TEM image, a boundary between pellets, that is, a grainboundary is not clearly observed in some cases. Thus, in the CAAC-OS, areduction in electron mobility due to the grain boundary is less likelyto occur.

FIG. 43A shows a high-resolution TEM image of a cross section of theCAAC-OS which is observed in the direction substantially parallel to thesample surface. The high-resolution TEM image is obtained with aspherical aberration corrector function. The high-resolution TEM imageobtained with a spherical aberration corrector function is particularlyreferred to as a Cs-corrected high-resolution TEM image. TheCs-corrected high-resolution TEM image can be observed with, forexample, an atomic resolution analytical electron microscope JEM-ARM200Fmanufactured by JEOL Ltd.

FIG. 43A shows pellets in which metal atoms are arranged in a layeredmanner. FIG. 43A proves that the size of a pellet is greater than orequal to 1 nm or greater than or equal to 3 nm. Therefore, the pelletcan also be referred to as a nanocrystal (nc). Furthermore, the CAAC-OScan also be referred to as an oxide semiconductor including c-axisaligned nanocrystals (CANC). A pellet reflects unevenness of a formationsurface or a top surface of the CAAC-OS and is parallel to the formationsurface or the top surface of the CAAC-OS.

FIGS. 43B and 43C show Cs-corrected high-resolution TEM images of aplane of the CAAC-OS observed in the direction substantiallyperpendicular to the sample surface. FIGS. 43D and 43E are imagesobtained by image processing of FIGS. 43B and 43C. The method of imageprocessing is as follows. The image in FIG. 43B is subjected to fastFourier transform (FFT) to obtain an FFT image. Then, mask processing isperformed on the obtained FFT image such that part in the range of 2.8nm⁻¹ to 5.0 nm⁻¹ from the reference point is left. After the maskprocessing, the FFT image is subjected to inverse fast Fourier transform(IFFT) to obtain a processed image. The image obtained in this manner isreferred to as an FFT filtering image. The FFT filtering image is aCs-corrected high-resolution TEM image from which a periodic componentis extracted and shows a lattice arrangement.

In FIG. 43D, a portion in which the lattice arrangement is broken isshown by dashed lines. A region surrounded by dashed lines correspondsto one pellet. The portion denoted by the dashed lines is a junction ofpellets. The dashed lines draw a hexagon, which means that the pellethas a hexagonal shape. Note that the shape of the pellet is not always aregular hexagon but is a non-regular hexagon in many cases.

In FIG. 43E, a dotted line denotes a portion between a region where alattice arrangement is well aligned and another region where a latticearrangement is well aligned, and dashed lines denote the directions ofthe lattice arrangements. A clear crystal grain boundary cannot beobserved even in the vicinity of the dotted line. When a lattice pointin the vicinity of the dotted line is regarded as a center andsurrounding lattice points are joined, a distorted hexagon, a distortedpentagon, or a distorted heptagon can be formed, for example. That is, alattice arrangement is distorted so that formation of a crystal grainboundary is inhibited. This is probably because the CAAC-OS can toleratedistortion owing to a low density of the atomic arrangement in an a-bplane direction, the interatomic bond distance changed by substitutionof a metal element, and the like.

As described above, the CAAC-OS has c-axis alignment, its pellets(nanocrystals) are connected in the a-b plane direction, and its crystalstructure has distortion. For this reason, the CAAC-OS can also bereferred to as an oxide semiconductor including a c-axis-aligneda-b-plane-anchored (CAA) crystal.

The CAAC-OS is an oxide semiconductor with high crystallinity. Entry ofimpurities, formation of defects, or the like might decrease thecrystallinity of an oxide semiconductor. This means that the CAAC-OS hasfew impurities and defects (e.g., oxygen vacancies).

Note that an impurity means an element other than the main components ofan oxide semiconductor, such as hydrogen, carbon, silicon, or atransition metal element. For example, an element (e.g., silicon) havingstronger bonding force to oxygen than a metal element constituting apart of an oxide semiconductor extracts oxygen from the oxidesemiconductor, which results in a disordered atomic arrangement andreduced crystallinity of the oxide semiconductor. A heavy metal such asiron or nickel, argon, carbon dioxide, or the like has a large atomicradius (or molecular radius), and thus disturbs the atomic arrangementof the oxide semiconductor and decreases crystallinity.

The characteristics of an oxide semiconductor having impurities ordefects might be changed by light, heat, or the like. Impuritiescontained in the oxide semiconductor might serve as carrier traps orcarrier generation sources, for example. For example, an oxygen vacancyin the oxide semiconductor might serve as a carrier trap or serve as acarrier generation source when hydrogen is captured therein.

The CAAC-OS having few impurities and oxygen vacancies is an oxidesemiconductor with a low carrier density (specifically, lower than8×10¹¹ cm⁻³, preferably lower than 1×10¹¹ cm³, further preferably lowerthan 1×10¹⁰ cm³, and higher than or equal to 1×10⁻⁹ cm³). Such an oxidesemiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.Thus, the CAAC-OS can be regarded as an oxide semiconductor havingstable characteristics.

<5-3. nc-OS>

Next, an nc-OS is described.

Analysis of an nc-OS by XRD is described. When the structure of an nc-OSis analyzed by an out-of-plane method, a peak indicating orientationdoes not appear. That is, a crystal of an nc-OS does not haveorientation.

For example, when an electron beam with a probe diameter of 50 nm isincident on a 34-nm-thick region of a thinned nc-OS including anInGaZnO₄ crystal in the direction parallel to the formation surface, aring-like diffraction pattern (nanobeam electron diffraction pattern)shown in FIG. 44A is observed. FIG. 44B shows a diffraction pattern(nanobeam electron diffraction pattern) obtained when an electron beamwith a probe diameter of 1 nm is incident on the same sample. In FIG.44B, a plurality of spots are observed in a ring-like region. Thus,ordering in an nc-OS is not observed with an electron beam with a probediameter of 50 nm but is observed with an electron beam with a probediameter of 1 nm.

When an electron beam with a probe diameter of 1 nm is incident on aregion with a thickness less than 10 nm, an electron diffraction patternin which spots are arranged in an approximately regular hexagonal shapeas shown in FIG. 44C is observed in some cases. This means that an nc-OShas a well-ordered region, that is, a crystal, in the thickness range ofless than 10 nm. Note that an electron diffraction pattern havingregularity is not observed in some regions because crystals are alignedin various directions.

FIG. 44D shows a Cs-corrected high-resolution TEM image of a crosssection of an nc-OS observed in the direction substantially parallel tothe formation surface. In the high-resolution TEM image, the nc-OS has aregion in which a crystal part is observed as indicated by additionallines and a region in which a crystal part is not clearly observed. Inmost cases, the size of a crystal part included in the nc-OS is greaterthan or equal to 1 nm and less than or equal to 10 nm, specificallygreater than or equal to 1 nm and less than or equal to 3 nm. Note thatan oxide semiconductor including a crystal part whose size is greaterthan 10 nm and less than or equal to 100 nm may be referred to as amicrocrystalline oxide semiconductor. In a high-resolution TEM image ofthe nc-OS, for example, a grain boundary is not clearly observed in somecases. Note that there is a possibility that the origin of thenanocrystal is the same as that of a pellet in a CAAC-OS. Therefore, acrystal part of the nc-OS may be referred to as a pellet in thefollowing description.

As described above, in the nc-OS, a microscopic region (for example, aregion with a size greater than or equal to 1 nm and less than or equalto 10 nm, in particular, a region with a size greater than or equal to 1nm and less than or equal to 3 nm) has a periodic atomic arrangement.There is no regularity of crystal orientation between different pelletsin the nc-OS. Thus, the orientation of the whole film is not observed.Accordingly, in some cases, the nc-OS cannot be distinguished from ana-like OS or an amorphous oxide semiconductor, depending on an analysismethod.

Since there is no regularity of crystal orientation between the pellets(nanocrystals), the nc-OS can also be referred to as an oxidesemiconductor including random aligned nanocrystals (RANC) or an oxidesemiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has higher regularity than anamorphous oxide semiconductor. Therefore, the nc-OS has a lower densityof defect states than the a-like OS and the amorphous oxidesemiconductor. Note that there is no regularity of crystal orientationbetween different pellets in the nc-OS. Therefore, the nc-OS has ahigher density of defect states than the CAAC-OS.

<5-4. a-like OS>

An a-like OS has a structure between the structure of an nc-OS and thestructure of an amorphous oxide semiconductor.

FIGS. 45A and 45B show high-resolution cross-sectional TEM images of ana-like OS. The high-resolution cross-sectional TEM image of the a-likeOS in FIG. 45A is taken at the start of the electron irradiation. Thehigh-resolution cross-sectional TEM image of the a-like OS in FIG. 45Bis taken after the irradiation with electrons (e⁻) at 4.3×10⁸ e⁻/nm².FIGS. 45A and 45B show that striped bright regions extending verticallyare observed in the a-like OS from the start of the electronirradiation. It can be also found that the shape of the bright regionchanges after the electron irradiation. Note that the bright region ispresumably a void or a low-density region.

The a-like OS has an unstable structure because it contains a void. Toverify that an a-like OS has an unstable structure as compared with aCAAC-OS and an nc-OS, a change in structure caused by electronirradiation is described below.

An a-like OS, an nc-OS, and a CAAC-OS are prepared as samples. Each ofthe samples is an In—Ga—Zn oxide.

First, a high-resolution cross-sectional TEM image of each sample isobtained. The high-resolution cross-sectional TEM images show that allthe samples have crystal parts.

It is known that a unit cell of an InGaZnO₄ crystal has a structure inwhich nine layers including three In—O layers and six Ga—Zn—O layers arestacked in the c-axis direction. The distance between the adjacentlayers is equivalent to the lattice spacing on the (009) plane (alsoreferred to as d value). The value is calculated to be 0.29 nm fromcrystal structural analysis. Accordingly, a portion in which the spacingbetween lattice fringes is greater than or equal to 0.28 nm and lessthan or equal to 0.30 nm is regarded as a crystal part of InGaZnO₄ inthe following description. Each lattice fringe corresponds to the a-bplane of the InGaZnO₄ crystal.

FIG. 46 shows a change in the average size of crystal parts (at 22points to 30 points) in each sample. Note that the crystal part sizecorresponds to the length of a lattice fringe. FIG. 46 indicates thatthe crystal part size in the a-like OS increases with an increase in thecumulative electron dose in obtaining TEM images, for example. As shownin FIG. 46, a crystal part with a size of approximately 1.2 nm (alsoreferred to as an initial nucleus) at the start of TEM observation growsto a size of approximately 1.9 nm at a cumulative electron (e) dose of4.2×10⁸ e⁻/nm². In contrast, the crystal part sizes in the nc-OS and theCAAC-OS show few changes from the start of electron irradiation to acumulative electron dose of 4.2×10⁸ e⁻/nm². As shown in FIG. 46, thecrystal part sizes in the nc-OS and the CAAC-OS are approximately 1.3 nmand approximately 1.8 nm, respectively, regardless of the cumulativeelectron dose. For the electron beam irradiation and TEM observation, aHitachi H-9000NAR transmission electron microscope was used. Theconditions of the electron beam irradiation were as follows: theaccelerating voltage was 300 kV; the current density was 6.7×10⁵e⁻/(nm²·s); and the diameter of an irradiation region was 230 nm.

In this manner, growth of the crystal part in the a-like OS may beinduced by electron irradiation. In contrast, in the nc-OS and theCAAC-OS, growth of the crystal part is hardly induced by electronirradiation. That is, the a-like OS has an unstable structure ascompared with the nc-OS and the CAAC-OS.

The a-like OS has a lower density than the nc-OS and the CAAC-OS becauseit contains a void. Specifically, the density of the a-like OS is higherthan or equal to 78.6% and lower than 92.3% of the density of thesingle-crystal oxide semiconductor having the same composition. Thedensity of the nc-OS and the density of the CAAC-OS are each higher thanor equal to 92.3% and lower than 100% of the density of thesingle-crystal oxide semiconductor having the same composition. It isdifficult to deposit an oxide semiconductor having a density lower than78% of the density of the single-crystal oxide semiconductor.

For example, in the case of an oxide semiconductor whose atomic ratio ofIn to Ga and Zn is 1:1:1, the density of single-crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor whose atomic ratio of In to Ga and Zn is1:1:1, the density of the a-like OS is higher than or equal to 5.0 g/cm³and lower than 5.9 g/cm³, for example. In the case of the oxidesemiconductor whose atomic ratio of In to Ga and Zn is 1:1:1, thedensity of the nc-OS and the density of the CAAC-OS are each higher thanor equal to 5.9 g/cm³ and lower than 6.3 g/cm³, for example.

In the case where an oxide semiconductor having a certain compositiondoes not exist in a single-crystal state, single-crystal oxidesemiconductors with different compositions are combined at an adequateratio, which makes it possible to calculate a density equivalent to thatof a single-crystal oxide semiconductor with the desired composition.The density of a single-crystal oxide semiconductor having the desiredcomposition may be calculated using a weighted average with respect tothe combination ratio of the single-crystal oxide semiconductors withdifferent compositions. Note that it is preferable to use as few kindsof single-crystal oxide semiconductors as possible to calculate thedensity.

As described above, oxide semiconductors have various structures andvarious properties. Note that an oxide semiconductor may be a stackedfilm including two or more of an amorphous oxide semiconductor, ana-like OS, an nc-OS, and a CAAC-OS, for example.

The structure described in this embodiment can be combined with any ofthe structures described in the other embodiments.

Embodiment 6

In this embodiment, a display module and electronic devices that includethe display device of one embodiment of the present invention aredescribed with reference to FIG. 47, FIGS. 48A to 48E, FIGS. 49A to 49E,and FIGS. 50A and 50B.

<6-1. Display Module>

In a display module 8000 illustrated in FIG. 47, a touch panel 8004connected to an FPC 8003, a display panel 8006 connected to an FPC 8005,a frame 8009, a printed board 8010, and a battery 8011 are providedbetween an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may overlap with the display panel 8006. Alternatively,a counter substrate (sealing substrate) of the display panel 8006 canhave a touch panel function. Alternatively, a photosensor may beprovided in each pixel of the display panel 8006 so as to function as anoptical touch panel.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can function asa radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or a power source using thebattery 8011 provided separately may be used. The battery 8011 can beomitted in the case of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

<6-2. Electronic Device>

FIGS. 48A to 48E and FIGS. 49A to 49E illustrate electronic devices.These electronic devices can include a housing 9000, a display portion9001, a camera 9002, a speaker 9003, an operation key 9005 (including apower switch or an operation switch), a connection terminal 9006, asensor 9007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared ray), a microphone 9008, and the like.

The electronic devices illustrated in FIGS. 48A to 48E and FIGS. 49A to49E can have a variety of functions, for example, a function ofdisplaying a variety of data (a still image, a moving image, a textimage, and the like) on the display portion, a touch panel function, afunction of displaying a calendar, date, time, and the like, a functionof controlling a process with a variety of software (programs), awireless communication function, a function of being connected to avariety of computer networks with a wireless communication function, afunction of transmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a memory medium and displaying the program or data on the displayportion, and the like. Note that functions of the electronic devicesillustrated in FIGS. 48A to 48E and FIGS. 49A to 49E are not limitedthereto, and the electronic devices may have other functions.

The electronic devices illustrated in FIGS. 48A to 48E and FIGS. 49A to49E are described in detail below.

FIG. 48A is a perspective view illustrating a television device 9100.The television device 9100 can include the display portion 9001 having alarge screen size of, for example, 50 inches or more, 80 inches or more,or 100 inches or more.

FIG. 48B, FIG. 48C, FIG. 48D, and FIG. 48E are perspective viewsillustrating a portable information terminal 9101, a portableinformation terminal 9102, a portable information terminal 9103, and aportable information terminal 9104, respectively.

The portable information terminal 9101 illustrated in FIG. 48B has, forexample, one or more of a function of a telephone set, a notebook, andan information browsing system. Specifically, the portable informationterminal 9101 can be used as a smartphone. Although not illustrated, thespeaker 9003, the connection terminal 9006, the sensor 9007, and thelike may be provided in the portable information terminal 9101. Theportable information terminal 9101 can display characters and imageinformation on its plurality of surfaces. For example, three operationbuttons 9050 (also referred to as operation icons or simply icons) canbe displayed on one surface of the display portion 9001. Furthermore,information 9051 indicated by dashed rectangles can be displayed onanother surface (for example, a side surface) of the display portion9001. Examples of the information 9051 include notification from asocial networking service (SNS), display indicating reception of ane-mail or an incoming call, the title of the e-mail, the SNS, or thelike, the sender of the e-mail, the SNS, or the like, the date, thetime, remaining battery, and the strength of a received signal.Alternatively, the operation buttons 9050 or the like may be displayedin place of the information 9051. The display portion 9001 of theportable information terminal 9101 partly has a curved surface.

The portable information terminal 9102 illustrated in FIG. 48C has afunction of displaying information, for example, on three or more sidesof the display portion 9001. Here, information 9052, information 9053,and information 9054 are displayed on different sides. For example, auser of the portable information terminal 9102 can see the display(here, the information 9053) with the portable information terminal 9102put in a breast pocket of his/her clothes. Specifically, a caller'sphone number, name, or the like of an incoming call is displayed in aposition that can be seen from above the portable information terminal9102. Thus, the user can see the display without taking out the portableinformation terminal 9102 from the pocket and decide whether to answerthe call. The display portion 9001 of the portable information terminal9102 partly has a curved surface.

Unlike in the portable information terminals 9101 and 9102 describedabove, the display portion 9001 does not have a curved surface in theportable information terminal 9103 illustrated in FIG. 48D.

The display portion 9001 of the portable information terminals 9104illustrated in FIG. 48E is curved. As illustrated in FIG. 48E, it ispreferable that the portable information terminal 9104 be provided witha camera 9002 to have a function of taking a still image, a function oftaking a moving image, a function of storing the taken image in a memorymedium (an external memory medium or a memory medium incorporated in thecamera), a function of displaying the taken image on the display portion9001, or the like.

FIG. 49A is a perspective view of a watch-type portable informationterminal 9200. FIG. 49B is a perspective view of a watch-type portableinformation terminal 9201.

The portable information terminal 9200 illustrated in FIG. 49A iscapable of executing a variety of applications such as mobile phonecalls, e-mailing, viewing and editing texts, music reproduction,Internet communication, and computer games. The display surface of thedisplay portion 9001 is bent, and images can be displayed on the bentdisplay surface. The portable information terminal 9200 can employ nearfield communication that is a communication method based on an existingcommunication standard. In that case, for example, mutual communicationbetween the portable information terminal 9200 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible. Moreover, the portable information terminal 9200 includes theconnection terminal 9006, and data can be directly transmitted to andreceived from another information terminal via a connector. Chargingthrough the connection terminal 9006 is possible. Note that the chargingoperation may be performed by wireless power feeding without using theconnection terminal 9006.

Unlike in the portable information terminal 9200 illustrated in FIG.49A, the display surface of the display portion 9001 is not curved inthe portable information terminal 9201 illustrated in FIG. 49B.Furthermore, the external state of the display portion of the portableinformation terminal 9201 is a non-rectangular shape (a circular shapein FIG. 49B).

FIGS. 49C, 49D, and 49E are perspective views of a foldable portableinformation terminal 9202. FIG. 49C is a perspective view illustratingthe portable information terminal 9202 that is opened. FIG. 49D is aperspective view illustrating the portable information terminal 9202that is being opened or being folded. FIG. 49E is a perspective viewillustrating the portable information terminal 9202 that is folded.

The folded portable information terminal 9202 is highly portable, andthe opened portable information terminal 9202 is highly browsable due toa seamless large display region. The display portion 9001 of theportable information terminal 9202 is supported by three housings 9000joined together by hinges 9055. By folding the portable informationterminal 9202 at a connection portion between two housings 9000 with thehinges 9055, the portable information terminal 9202 can be reversiblychanged in shape from opened to folded. For example, the portableinformation terminal 9202 can be bent with a radius of curvature ofgreater than or equal to 1 mm and less than or equal to 150 mm.

The display device which is one embodiment of the present invention canbe preferably used for the display portion 9001.

FIGS. 50A and 50B are perspective views of a display device 9500including a plurality of display panels. Note that the plurality ofdisplay panels are wound in the perspective view in FIG. 50A, and areunwound in the perspective view in FIG. 50B.

The display device 9500 illustrated in FIGS. 50A and 50B includes aplurality of display panels 9501, a hinge 9511, and a bearing 9512. Theplurality of display panels 9501 each include a display region 9502 anda light-transmitting region 9503.

Each of the plurality of display panels 9501 is flexible. Two adjacentdisplay panels 9501 are provided so as to partly overlap with eachother. For example, the light-transmitting regions 9503 of the twoadjacent display panels 9501 can be overlapped each other. A displaydevice having a large screen can be obtained with the plurality ofdisplay panels 9501. The display device is highly versatile because thedisplay panels 9501 can be wound depending on its use.

Moreover, although the display regions 9502 of the adjacent displaypanels 9501 are separated from each other in FIGS. 50A and 50B, withoutlimitation to this structure, the display regions 9502 of the adjacentdisplay panels 9501 may overlap with each other without any space sothat a continuous display region 9502 is obtained, for example.

The display device of one embodiment of the present invention can bepreferably used in the display panel 9501.

Electronic devices described in this embodiment are characterized byhaving a display portion for displaying some sort of information. Notethat the semiconductor device of one embodiment of the present inventioncan also be used for an electronic appliance that does not have adisplay portion.

The structure described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 7

In this embodiment, the structure of a data processor including thedisplay device of one embodiment of the present invention is describedwith reference to FIGS. 51A and 51B.

FIG. 51A is a block diagram illustrating the structure of a dataprocessor 9600 including the display device of one embodiment of thepresent invention. FIG. 51B is a schematic diagram illustrating the dataprocessor 9600 being in operation.

The following describes components of the data processor 9600. In somecases, the components cannot be clearly distinguished from each otherand one component also serves as another component or includes part ofanother component.

<7. Structure Example of Data Processor>

The data processor 9600 includes an arithmetic device 9610 and aninput/output device 9620.

[Arithmetic Unit]

The arithmetic device 9610 includes an arithmetic portion 9611, a memoryportion 9612, a transmission path 9614, and an input/output interface9615.

[Arithmetic Portion]

The arithmetic portion 9611 has a function of executing a program.

[Memory Portion]

The memory portion 9612 has a function of storing a program executed bythe arithmetic portion 9611, initial information, setting information,an image, or the like. Specifically, a hard disk, a flash memory, amemory including a transistor formed using an oxide semiconductor, orthe like can be used as the memory portion 9612.

[Program]

A program is executed by the arithmetic portion 9611 through three stepsdescribed below with reference to FIG. 51B, for example.

In a first step, positional data P1 is acquired.

In a second step, a first region 9681 is determined on the basis of thepositional data P1.

In a third step, an image (image data Q1) with higher luminance than animage displayed on a region other than the first region 9681 is producedas an image displayed on the first region 9681.

For example, the arithmetic device 9610 determines the first region 9681on the basis of the positional data P1. The first region 9681 can have,specifically, an elliptical shape, a circular shape, a polygonal shape,a rectangular shape, or the like. A region within a 60-cm radius,preferably within a 5-30-cm radius, from the positional data P1 isdetermined as the first region 9681, for example.

To produce an image with higher luminance than an image displayed on aregion other than the first region 9681 as an image displayed on thefirst region 9681, the luminance of the image displayed on the firstregion 9681 is increased to 110% or more, preferably 120% or more and200% or less, of the luminance of the image displayed on the regionother than the first region 9681. Alternatively, the average luminanceof the image displayed on the first region 9681 is increased to 110% ormore, preferably 120% or more and 200% or less, of the average luminanceof the image displayed on the region other than the first region 9681.

As a result of the program, the data processor 9600 can generate theimage data Q1 with higher luminance than an image displayed on a regionother than the first region 9681 as an image displayed on the firstregion 9681 on the basis of the positional data P1. Consequently, thedata processor 9600 can have high convenience and can provide operatorswith comfortable operation.

[Input/Output Interface]

The input/output interface 9615 includes a terminal or a wiring. Theinput/output interface 9615 has a function of supplying data and afunction of receiving data. The input/output interface 9615 can beelectrically connected to the transmission path 9614 and/or theinput/output device 9620, for example.

[Transmission Path]

The transmission path 9614 includes a wiring. The transmission path 9614has a function of supplying data and a function of receiving data. Thetransmission path 9614 can be electrically connected to the arithmeticportion 9611, the memory portion 9612, or the input/output interface9615, for example.

[Input/Output Device]

The input/output device 9620 includes a display portion 9630, an inputportion 9640, a sensor portion 9650, and a communication portion 9690.

[Display Portion]

The display portion 9630 includes a display panel. The display panelincludes a pixel having a structure including a reflective displayelement and a transmissive light-emitting element. The luminance of adisplayed image can be increased by increasing the reflectance of thereflective display element or the luminance of the light-emittingelement with the use of the image data. That is, the display device ofone embodiment of the present invention can be preferably used in thedisplay portion 9630.

[Input Portion]

The input portion 9640 includes an input panel. The input panelincludes, for example, a proximity sensor. The proximity sensor has afunction of sensing a pointer 9682. Note that a finger, a stylus pen, orthe like can be used as the pointer 9682. For the stylus pen, alight-emitting element such as a light-emitting diode, a metal piece, acoil, or the like can be used.

As the proximity sensor, a capacitive proximity sensor, anelectromagnetic inductive proximity sensor, an infrared proximitysensor, a proximity sensor including a photoelectric conversion element,or the like can be used.

The capacitive proximity sensor includes a conductive film and has afunction of sensing the proximity to the conductive film. To determinepositional data, for example, a plurality of conductive films areprovided in different regions of the input panel and a region where afinger or the like used as the pointer 9682 approaches can be determinedin accordance with a change in parasitic capacitance of the conductivefilms.

The electromagnetic inductive proximity sensor includes a function ofsensing the proximity of a metal piece, a coil, or the like to a sensorcircuit. To determine positional data, for example, a plurality ofoscillation circuits are provided in different regions of the inputpanel and a region where a metal piece, a coil, or the like included ina stylus pen or the like used as the pointer 9682 approaches can bedetermined in accordance with a change in the circuit constant of theoscillation circuits.

The photo-detection proximity sensor has a function of sensing theproximity of a light-emitting element. To determine positional data, forexample, a plurality of photoelectric conversion elements are providedin different regions of the input panel and a region where alight-emitting element included in a stylus pen or the like used as thepointer 9682 approaches can be determined in accordance with a change inthe electromotive force of the photoelectric conversion elements.

[Sensor Portion]

As the sensor portion 9650, an illuminance sensor that senses theenvironmental brightness, a human motion sensor, or the like can beused.

[Communication Portion]

The communication portion 9690 has a function of supplying data to anetwork and acquiring data from the network.

The data processor 9600 described above can be used for education, orcan be used for a digital signage or a smart television system, forexample.

Note that this embodiment can be combined with any of the otherembodiments in this specification as appropriate.

Example 1

In Example 1, examples of fabricating light-emitting elements that canbe used in the display device of one embodiment of the present inventionare described. Note that in Example 1, a light-emitting element 1, alight-emitting element 2, and a light-emitting element 3 werefabricated.

FIGS. 52A, 52B, and 52C are schematic cross-sectional views of thelight-emitting element 1, the light-emitting element 2, and thelight-emitting element 3, respectively. Table 1 lists detailed elementstructures of the light-emitting elements 1 to 3, and structures andabbreviations of compounds used for the light-emitting elements areshown below.

TABLE 1 Thickness Layer Reference (nm) Material Weight ratio Light-Upper electrode 714 200 Al — emitting Electron-injection layer 734 1 LiF— element 1 Electron-transport layer (2) 733(2) 15 NBphenElectron-transport layer (1) 733(1) 5 cgDBCzPA — Light-emitting layer b710b 25 cgDBCzPA:1,6BnfAPm-03 1:0.05 Light-emitting layer a 710a 302mDBTBPDBq-II:PCBBiF:Ir(dmdppr-dmp)₂(acac) 0.8:0.2:0.06 Hole-transportlayer 732 20 PCPPn — Hole-injection layer 731 35 PCPPn:MoOx 2:1   Lowerelectrode 704 70 ITSO — Light- Upper electrode 714 200 Al — emittingElectron-injection layer 734 1 LiF — element 2 Electron-transport layer(2) 733(2) 15 NBphen Electron-transport layer (1) 733(1) 5 cgDBCzPA —Light-emitting layer b 710b 25 cgDBCzPA:1,6BnfAPm-03 1:0.05Light-emitting layer a(2) 710a(2) 10 2mDBTBPDBq-II:Ir(tBuppm)₂(acac)0.7:0.06 Light-emitting layer a(1) 710a(1) 202mDBTBPDBq-II:PCBBiF:Ir(tBuppm)₂(acac) 0.7:0.3:0.06 Hole-transport layer732 20 PCPPn — Hole-injection layer 731 35 PCPPn:MoOx 2:1   Lowerelectrode 704 70 ITSO — Light- Upper electrode 714 200 Al — emittingElectron-injection layer 734 1 LiF — element 3 Electron-transport layer(2) 733(2) 15 NBphen Electron-transport layer (1) 733(1) 5 cgDBCzPA —Light-emitting layer b 710b 25 cgDBCzPA:1,6BnfAPm-03 1:0.05Hole-transport layer 732 20 PCPPn — Hole-injection layer 731 35PCPPn:MoOx 2:1   Lower electrode 704 70 ITSO —

<1-1. Method for Fabricating Light-Emitting Element 1>

First, over a substrate 702, an ITSO film was formed as a lowerelectrode 704 by a sputtering method. Note that the thickness of thelower electrode 704 was 70 nm, and the area of the lower electrode 704was 4 mm² (2 mm×2 mm).

Then, for pretreatment before deposition of an organic compound layer byevaporation, the lower electrode 704 side of the substrate 702 waswashed with water, baking was performed at 200° C. for 1 hour, and thenUV ozone treatment was performed on a surface of the lower electrode 704for 370 seconds.

After that, the substrate 702 was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 60 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 702 was cooled down for approximately 30 minutes.

Next, the substrate 702 was fixed to a holder provided in the vacuumevaporation apparatus such that a surface of the substrate over whichthe lower electrode 704 was formed faced downward.

In the light-emitting element 1, by a vacuum evaporation method, ahole-injection layer 731, a hole-transport layer 732, a light-emittinglayer 710 a, a light-emitting layer 710 b, an electron-transport layer733(1), an electron-transport layer 733(2), an electron-injection layer734, and an upper electrode 714 were sequentially formed. Thefabrication method is described in detail below.

First, the pressure in a vacuum apparatus was reduced to 10⁻⁴ Pa,followed by formation of the hole-injection layer 731 over the lowerelectrode 704. For the hole-injection layer 731,9-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]phenanthrene (abbreviation:PCPPn) and molybdenum oxide were deposited by co-evaporation such thatthe weight ratio of PCPPn to molybdenum oxide was 2:1. The thickness ofthe hole-injection layer 731 was 35 nm.

Then, the hole-transport layer 732 was formed on the hole-injectionlayer 731. As the hole-transport layer 732, PCPPn was deposited byevaporation. The thickness of the hole-transport layer 732 was 20 nm.

Next, the light-emitting layer 710 a was formed over the hole-transportlayer 732. The light-emitting layer 710 a was formed by co-evaporationof 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),N-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluoren-2-amine (abbreviation: PCBBiF), andbis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(dmdppr-dmp)₂(acac)) with a weight ratio of2mDBTBPDBq-II to PCBBiF and Ir(dmdppr-dmp)₂(acac)=0.8:0.2:0.06. Notethat the thickness of the light-emitting layer 710 a was 30 nm. In thelight-emitting layer 710 a, 2mDBTBPDBq-II is a host material, PCBBiF isan assist material, and Ir(dmdppr-dmp)₂(acac) is a phosphorescentmaterial (a guest material).

Next, the light-emitting layer 710 b was formed over the light-emittinglayer 710 a. The light-emitting layer 710 b was formed by co-evaporationof 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) andN,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPrn-03) at a weight ratio of 1:0.05 (=cgDBCzPA:1,6BnfAPrn-03). The thickness of the light-emitting layer 710 b was 25nm. Note that cgDBCzPA was the host material and 1,6BnfAPrn-03 was thefluorescent material (the guest material) in the light-emitting layer710 b.

Next, on the light-emitting layer 710 b, the electron-transport layer733(1) was formed by evaporation of cgDBCzPA to a thickness of 5 nm.Then, on the electron-transport layer 733(1), the electron-transportlayer 733(2) was formed by evaporation of2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBphen) to a thickness of 15 nm. Then, on the electron-transport layer733(2), the electron-injection layer 734 was formed by evaporation oflithium fluoride (LiF) to a thickness of 1 nm.

Then, on the electron-injection layer 734, a 200-nm-thick aluminum filmwas formed as the upper electrode 714.

Through the above steps, the light-emitting element over the substrate702 was formed.

Next, the light-emitting element over the substrate 702 was sealed bybeing bonded to a sealing substrate (not illustrated) in a glove box ina nitrogen atmosphere so as not to be exposed to the air (specifically,a sealant was applied to surround the element, and irradiation withultraviolet light having a wavelength of 365 nm at 6 J/cm² and heattreatment at 80° C. for one hour were performed for sealing).

Through the above process, the light-emitting element 1 was fabricated.

<1-2. Method for Fabricating Light-Emitting Element 2>

The light-emitting element 2 was fabricated through the same steps asthose for the above-described light-emitting element 1 except stepsdescribed below.

A light-emitting layer 710 a(1) was formed over the hole-transport layer732. The light-emitting layer 710 a(1) was formed by co-evaporation of2mDBTBPDBq-II, PCBBiF, and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) at a mass ratio of 0.7:0.3:0.06(=2mDBTBPDBq-II: PCBBiF: [Ir(tBuppm)₂(acac)]). The thickness of thelight-emitting layer 710 a(1) was 20 nm. Note that 2mDBTBPDBq-II was thehost material, PCBBiF was the assist material, and Ir(tBuppm)₂(acac) wasthe phosphorescent material (the guest material) in the light-emittinglayer 710 a(1).

Next, the light-emitting layer 710 a(2) was formed over thelight-emitting layer 710 a(1). The light-emitting layer 710 a(2) wasformed by co-evaporation of 2mDBTBPDBq-II and Ir(tBuppm)₂(acac) at aweight ratio of 0.7:0.06 (=2mDBTBPDBq-II: Ir(tBuppm)₂(acac)). Thethickness of the light-emitting layer 710 a(2) was 10 nm. Note that2mDBTBPDBq-II was the host material and Ir(tBuppm)₂(acac) was thephosphorescent material (the guest material) in the first light-emittinglayer 710 a(2).

<1-3. Method for Fabricating Light-Emitting Element 3>

The light-emitting element 3 was fabricated through the same steps asthose for the above-described light-emitting element 1 except stepsdescribed below.

The light-emitting layer 710 b was formed over the hole-transport layer732. The light-emitting layer 710 b was formed by co-evaporation ofcgDBCzPA and 1,6BnfAPrn-03 at a weight ratio of 1:0.05 (=cgDBCzPA:1,6BnfAPrn-03). The thickness of the light-emitting layer 710 b was 25nm. Note that cgDBCzPA was the host material and 1,6BnfAPrn-03 was thefluorescent material (the guest material) in the light-emitting layer710 b.

Note that in all the above evaporation steps for the light-emittingelements 1 to 3, a resistance heating method was used as an evaporationmethod.

<1-3. Characteristics of Light-Emitting Elements 1 to 3>

FIG. 53, FIG. 54, FIG. 55, and FIG. 56 show luminance-current densitycharacteristics, luminance-voltage characteristics, currentefficiency-luminance characteristics, and current-voltagecharacteristics, respectively, of the light-emitting elements 1 to 3.Note that the characteristics of the light-emitting elements weremeasured at room temperature (in an atmosphere kept at 25° C.).

Table 2 shows element characteristics of the light-emitting elements 1to 3 at around 1000 cd/m².

TABLE 2 Chromaticity Current External quantum Voltage Current Currentdensity coordinates Luminance efficiency efficiency (V) (mA) (mA/cm²)(x, y) (cd/m²) (cd/A) (%) Light-emitting 3.3 0.09 2.4 (0.66, 0.34) 90938.4 26.0 element 1 Light-emitting 3.0 0.03 0.7 (0.41, 0.59) 910 125.432.4 element 2 Light-emitting 3.0 0.30 7.6 (0.14, 0.10) 716 9.5 10.9element 3

FIG. 57 shows emission spectra when a current at a current density of2.5 mA/cm² was supplied to the light-emitting elements 1 to 3. As shownin FIG. 57, an emission spectrum of the light-emitting element 1 has apeak in the red wavelength range, an emission spectrum of thelight-emitting element 2 has a peak in the green wavelength range, andan emission spectrum of the light-emitting element 3 has a peak in theblue wavelength range.

As shown in Table 2, FIG. 53 to FIG. 57, the light-emitting elements 1to 3 each have element characteristics having high efficiency and lightemission in a desired wavelength range. Moreover, it is found that, ineach of the light-emitting elements 1 and 2, the guest material in thelight-emitting layer 510 b does not contribute to light emission.

The structure described in Example 1 can be used in appropriatecombination with any of the structures described in the other exampleand the embodiments.

Example 2

In Example 2, examples of fabricating light-emitting elements that canbe used in the display device of one embodiment of the present inventionare described. Note that in Example 2, a light-emitting element 4, alight-emitting element 5, and a light-emitting element 6 werefabricated.

FIGS. 58A, 58B, and 58C are schematic cross-sectional views of thelight-emitting element 4, the light-emitting element 5, and thelight-emitting element 6, respectively.

The light-emitting element 4 has a structure in which a color film751(R) is provided in the light-emitting element 1. The light-emittingelement 5 has a structure in which a color film 751(G) is provided inthe light-Emitting element 2. The light-emitting element 6 has astructure in which a color film 751(B) is provided in the light-emittingelement 3. Materials, manufacturing methods, and the like used for thelight-emitting elements 4 to 6 were the same as those used for thelight-emitting elements 1 to 3 described in Example 1.

The color film 751(R) was a color filter that transmits light in a redwavelength range, the color film 751(G) was a color filter thattransmits light in a green wavelength range, and the color film 751(B)was a color filter that transmits light in a blue wavelength range.

<2. Characteristics of Light-Emitting Elements 4 to 6>

FIG. 59, FIG. 60, FIG. 61, and FIG. 62 show luminance-current densitycharacteristics, luminance-voltage characteristics, currentefficiency-luminance characteristics, and current-voltagecharacteristics, respectively, of the light-emitting elements 4 to 6.Note that the characteristics of the light-emitting elements weremeasured at room temperature (in an atmosphere kept at 25° C.).

Table 3 shows element characteristics of the light-emitting elements 4to 6 at around 1000 cd/m².

TABLE 3 Current Chromaticity Current External quantum Voltage Currentdensity coordinates Luminance efficiency efficiency (V) (mA) (mA/cm²)(x, y) (cd/m²) (cd/A) (%) Light-emitting 3.4 0.16 3.9 (0.68, 0.32) 91723.5 20.0 element 4 Light-emitting 3.1 0.06 1.4 (0.33, 0.66) 887 62.914.2 element 5 Light-emitting 3.1 0.57 14.3 (0.14, 0.08) 890 6.2 8.9element 6

FIG. 63 shows emission spectra when a current at a current density of2.5 mA/cm² was supplied to the light-emitting elements 4 to 6. As shownin FIG. 63, an emission spectrum of the light-emitting element 4 has apeak in the red wavelength range, an emission spectrum of thelight-emitting element 5 has a peak in the green wavelength range, andan emission spectrum of the light-emitting element 6 has a peak in theblue wavelength range.

As shown in Table 3, FIG. 59 to FIG. 63, the light-emitting elements 4to 6 each have element characteristics having high efficiency and lightemission in a desired wavelength range. Moreover, it is found that, ineach of the light-emitting elements 4 and 5, the guest material in thelight-emitting layer 710 b does not contribute to light emission.

The light-emitting elements 4 to 6 include the color film 756(R), thecolor film 756(G), and the color film 756(B), respectively, and thushave higher color purities than the light-emitting elements 1 to 3described in Example 1. However, the light-emitting elements 4 to 6 havelower current efficiency and external quantum efficiency owing to thecolor films (the color film 756(R), the color film 756(G), and the colorfilm 756(B)). Therefore, the optimum element structure may be selectedby a practitioner.

The structure described in Example 2 can be used in appropriatecombination with any of the structures described in the other exampleand the embodiments.

EXPLANATION OF REFERENCE

-   10: pixel, 11: display element, 11 d: display region, 12: display    element, 12 d: display region, 12B: light-emitting element, 12G:    light-emitting element, 12R: light-emitting element, 100:    transistor, 100A: transistor, 100F: transistor, 100G: transistor,    100H: transistor, 100J: transistor, 100K: transistor, 102:    substrate, 104: insulating film, 106: conductive film, 108: oxide    semiconductor film, 108_1: oxide semiconductor film, 108_2: oxide    semiconductor film, 108_3: oxide semiconductor film, 108 d: drain    region, 108 i: channel region, 108 s: source region, 110: insulating    film, 112: conductive film, 116: insulating film, 118: insulating    film, 120 a: conductive film, 120 b: conductive film, 141 a:    opening, 141 b: opening, 143: opening, 300A: transistor, 300B:    transistor, 300C: transistor, 300D: transistor, 300E: transistor,    300F: transistor, 302: substrate, 304: conductive film, 306:    insulating film, 307: insulating film, 308: oxide semiconductor    film, 308_1: oxide semiconductor film, 308_2: oxide semiconductor    film, 308_3: oxide semiconductor film, 312 a: conductive film, 312    b: conductive film, 314: insulating film, 316: insulating film, 318:    insulating film, 320 a: conductive film, 320 b: conductive film, 341    a: opening, 341 b: opening, 342 a: opening, 342 b: opening, 342 c:    opening, 401: substrate, 402: conductive film, 403 a: conductive    film, 403 b: conductive film, 403 c: conductive film, 404:    insulating film, 405 a: conductive film, 405 b: conductive film, 405    c: conductive film, 405 d: conductive film, 406: insulating film,    407 a: conductive film, 407 b: conductive film, 407 c: conductive    film, 407 d: conductive film, 407 e: conductive film, 407 f:    conductive film, 407 g: conductive film, 408: insulating film, 409    a: oxide semiconductor film, 409 b: oxide semiconductor film, 409 c:    oxide semiconductor film, 410 a: insulating film, 410 b: insulating    film, 410 c: insulating film, 411 a: oxide semiconductor film, 411    b: oxide semiconductor film, 411 c: oxide semiconductor film, 412:    insulating film, 413: insulating film, 414 a: conductive film, 414    b: conductive film, 414 c: conductive film, 414 d: conductive film,    414 e: conductive film, 414 f: conductive film, 414 g: conductive    film, 414 h: conductive film, 416: insulating film, 417: conductive    film, 417B: conductive film, 417G: conductive film, 417R: conductive    film, 418: insulating film, 419: EL layer, 420: conductive film,    450: opening, 452: substrate, 454: sealing material, 481: shadow    mask, 482: opening, 500: display device, 502: pixel portion, 504 a:    gate driver circuit portion, 504 b: gate driver circuit portion,    506: source driver circuit portion, 508 a: external circuit, 508 b:    external circuit, 510 b: light-emitting layer, 602: light-blocking    film, 604: color film, 606: insulating film, 608: conductive film,    610 a: structure body, 610 b: structure body, 618 a: alignment film,    618 b: alignment film, 620: liquid crystal layer, 622: sealant, 624:    conductor, 626: functional film, 652: substrate, 662: light-blocking    film, 663: insulating film, 664: electrode, 665: electrode, 666:    insulating film, 667: electrode, 668: insulating film, 670:    substrate, 672: substrate, 674: bonding material, 681: insulating    film, 682: conductive film, 691: touch panel, 692: touch panel, 693:    touch panel, 702: substrate, 704: lower electrode, 710 a:    light-emitting layer, 710 b: light-emitting layer, 714: upper    electrode, 731: hole-injection layer, 732: hole-transport layer,    733: electron-transport layer, 734: electron-injection layer, 751:    color film, 756: color film, 8000: display module, 8001: upper    cover, 8002: lower cover, 8003: FPC, 8004: touch panel, 8005: FPC,    8006: display panel, 8009: frame, 8010: printed substrate, 8011:    battery, 9000: housing, 9001: display portion, 9002: camera, 9003:    speaker, 9005: operation key, 9006: connection terminal, 9007:    sensor, 9008: microphone, 9050: operation button, 9051: information,    9052: information, 9053: information, 9054: information, 9055:    hinge, 9100: television device, 9101: partable information terminal,    9102: partable information terminal, 9103: partable information    terminal, 9104: partable information terminal, 9200: partable    information terminal, 9201: partable information terminal, 9202:    partable information terminal, 9500: display device, 9501: display    panel, 9502: display region, 9503: region, 9511: axis portion, 9512:    bearing, 9600: data processor, 9610: arithmetic device, 9611:    arithmetic portion, 9612: memory portion, 9614: transmission path,    9615: input/output interface, 9620: input/output device, 9630:    display portion, 9640: input portion, 9650: sensor portion, 9681:    region, 9682: pointer, 9690: communication portion

This application is based on Japanese Patent Application serial no.2015-195939 filed with Japan Patent Office on Oct. 1, 2015, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising: a first pixel; and a second pixel,wherein the first pixel and the second pixel are adjacent to each other,wherein each of the first pixel and the second pixel comprises a firstdisplay region and a second display region, wherein the first displayregion is configured to reflect incident light, wherein the seconddisplay region is positioned inside the first display region andconfigured to emit light, and wherein a position of the second displayregion inside the first display region in the first pixel and a positionof the second display region inside the first display region in thesecond pixel are different from each other.
 2. The display deviceaccording to claim 1, wherein an interval between the second displayregion in the first pixel and the second display region in the secondpixel is greater than or equal to 20 μm.
 3. A display module comprising:the display device according to claim 1; and a touch sensor.
 4. Anelectronic device comprising: the display device according to claim 1;and a battery.
 5. A display device comprising: a first pixel; and asecond pixel, wherein the first pixel and the second pixel are adjacentto each other, wherein each of the first pixel and the second pixelcomprises a first display region, a second display region, a firstdisplay element, and a second display element, wherein the first displayregion is configured to reflect incident light, wherein the seconddisplay region is positioned inside the first display region andconfigured to emit light, wherein the first display element overlapswith the first display region, wherein the second display elementoverlaps with the second display region, and wherein a position of thesecond display region inside the first display region in the first pixeland a position of the second display region inside the first displayregion in the second pixel are different from each other.
 6. The displaydevice according to claim 5, wherein the first display element comprisesa liquid crystal layer, and wherein the second display element comprisesa light-emitting layer.
 7. The display device according to claim 5,wherein colors of light emitted from the second display element in thefirst pixel and the second display element in the second pixel aredifferent.
 8. The display device according to claim 5, wherein the firstdisplay element and the second display element are connected todifferent transistors and independently controlled.
 9. The displaydevice according to claim 8, wherein each of the transistors comprisesan oxide semiconductor film in a channel region.
 10. The display deviceaccording to claim 5, wherein an interval between the second displayregion in the first pixel and the second display region in the secondpixel is greater than or equal to 20 μm.
 11. A display modulecomprising: the display device according to claim 5; and a touch sensor.12. An electronic device comprising: the display device according toclaim 5; and a battery.
 13. A display device comprising: a first pixel;and a second pixel, wherein the first pixel and the second pixel areadjacent to each other, wherein each of the first pixel and the secondpixel comprises a first display element and a second display element,wherein the first display element comprises a reflective film includingan opening, wherein the second display element comprises alight-emitting layer, wherein the opening overlaps with thelight-emitting layer, and wherein a position of the opening in the firstpixel and a position of the opening in the second pixel are differentfrom each other.
 14. The display device according to claim 13, whereinthe first display element comprises a liquid crystal layer.
 15. Thedisplay device according to claim 13, wherein colors of light emittedfrom the second display element in the first pixel and the seconddisplay element in the second pixel are different.
 16. The displaydevice according to claim 13, wherein the first display element and thesecond display element are connected to different transistors andindependently controlled.
 17. The display device according to claim 16,wherein each of the transistors comprises an oxide semiconductor film ina channel region.
 18. The display device according to claim 13, whereinan interval between the opening in the first pixel and the opening inthe second pixel is greater than or equal to 20 μm.
 19. A display modulecomprising: the display device according to claim 13; and a touchsensor.
 20. An electronic device comprising: the display deviceaccording to claim 13; and a battery.